Relative being the keyword here. From 1500 to 1600 there was a shift away from heavily armored gendarmes and the increasing dominance of pike and shot tactics; from 1600 to 1700 was the shifting away from armor almost entirely and the decline of the pike, so in comparison 115 years of men lining up and shooting at each other with flintlocks seems like progress stalled right?
I am aware there were tactical doctrine changes such as the many Napoleon brought about but even still it pales in comparison to prior centuries, at least to a layman. Did anyone at that time notice or comment on this, or suggest radical changes?
We tend to approach the period of around 1700 to 1815 as one of unchanging linear warfare, but this impression is wrong. Now, there are answers on this subreddit that go into the tactical and operational changes that took place from the French Revolution onward, such as these by /u/dandan_noodles:
So I will specifically address things that went on between around 1700 and 1790. I'm not a specialist in this period but I've read up on it in the past (although I appreciate that some of this scholarship is older and may have been superceded), so I will own up to any errors or omissions that are pointed out.
A focus purely on standard-issue infantry small arms obscures some rather noticeable technological developments, particularly in the field of artillery. One of the more noted developments of the period was the Gribeauval system introduced in 1765, which saw the French field artillery standardised to four calibres, and which also involved the guns being produced through machining by drilling out the bore rather than being cast with a void using a disposable clay core, allowing for more precise manufacture and a lighter end product. But Gribeauval was not the first artillery standardiser, merely one of the more comprehensive as well as being the first to introduce bore-drilling. Within France he was already building off standardisation attempts made by Vallière in the 1730s, while Austria saw its own attempt at artillery standardisation with the Liechtenstein system in the 1750s. These standardisations did not simply incrementally alter the efficiency of artillery, but also saw a move towards generally lighter calibres that were more suited to the conditions of field battles, which demanded greater mobility and higher, sustained rates of fire. You could carry more ammo for guns of smaller calibre, and lighter guns in general were easier to move.
In addition, the solid shot-firing field cannon was not the only gun type in use, as the former half of the eighteenth century also saw the rise of the explosive shell-firing howitzer. This had been introduced by the Dutch as a siege weapon in the 1690s, but its viability as a battlefield weapon soon became apparent. Because they fired explosive shells in a relatively high arc, howitzers essentially allowed for indirect fire, and so threatened troops in built-up areas or field fortifications who were otherwise well-protected from direct fire guns, diminishing the effectiveness of holding such strongpoints. But howitzers also derived their field potential from their usefulness as a platform for firing canister, a short-range anti-personnel munition consisting essentially of musket rounds that would end up being dispersed across a wide area. The wide bore and short barrel of the howitzer meant that it fired an especially large number of rounds across an especially wide dispersion. This latter role was so substantial that one particularly enterprising Russian ordnance master, Pyotr Shuvalov, developed a gun which he called the 'secret howitzer' designed as a canister-only platform, using a rather creative oval bore shape in an attempt to improve the horizontal dispersion of canister shot. It wasn't very good (nor were his attempts at light field mortars), although another of Shuvalov's introductions, the 'unicorn', paved the way for future developments (once its kinks were ironed out). Able to fire solid shot, shells, and canister, the unicorn was versatile enough that the basic pattern remained in service through the Crimean War in the 1850s.
It's not for nothing that the mid-18th century has been said by some to have seen an 'artillery revolution'. While some reformers (Gribeauval and Liechtenstein) were more successful than others (Shuvalov), they all represent armies attempting to refine their artillery arms considerably. Indeed, they were also trying to expand them. During the War of the Spanish Succession (1701-14), armies brought an average of around one gun per 1000 men; by the time of the War of the Austrian Succession (1740-48) it was usually two or more; by the Seven Years' War (1754/6-63) they brought at least three and typically five or more. Even if the infantry were still firing at each other in line with flintlocks, they were being hammered by five times more artillery in the middle of the period compared to the start.
While field artillery was the big beneficiary of technological improvement, it would be remiss not to also bring up the arrival of a specialist weapon in the infantry arm, that being the Jäger rifle. The pop culture image of the American War of Tax Avoidance Independence is that of British musketeers in line fighting American riflemen in loose order, but the British also fielded riflemen of their own, from two sources. The first were the Jäger of Britain's Hessian allies, and the second were riflemen within the British army's own light infantry elements, equipped with the Pattern 1776 Rifle patterned after German designs. The long rifles used by the American rebels were, to be frank, not battlefield weapons: to make effective use of the rifling you had to minimise 'windage' (the gap between the bullet and the bore of the weapon) and so the bullet and its patch were an intentionally tight fit that took a long time to force down. A well-trained musketeer could fire and reload two, three, or even four times in the time it took to reload a long rifle. The Jäger rifle, developed in the German states, essentially compromised by having a short barrel that was much faster to ram a patch and ball down, while still having a considerable advantage in accuracy over a smoothbore musket. It would also become the pattern for the later Baker Rifle of the Napoleonic Wars issued to specialist light troops in the British army, the King's German Legion, and the Portuguese army. (And, of course, Jäger rifles remained in use among the armies of the German states.)
I have alluded above to this already, but it simply cannot be understated how substantial the shift in the very ethos of military tactics was in the latter half of the eighteenth century. The (re?)emergence of light troops in European warfare, while often considered a feature of the French Revolutionary and Napoleonic Wars or as a reaction to American tactics in the 1770s, in fact had its origins early in the century, with a major contributor being experience from the Habsburg monarchy's wars against the Ottomans in the Balkans, although one could argue that similar shifts in North America were driven specifically by adaptation to Native American tactics. The Balkan campaigns saw the Habsburg armies make considerable use of light infantry, of whom the most notable were the Croatian Grenzer, and of light cavalry, most prominently the Hungarian Hussars. In turn, these saw emulation to greater or lesser extents in European armies, some of which shared the Habsburgs' approach of recruiting from certain cultural groups perceived as more experienced (or, in proto-racial terms, better suited) to such forms of warfare. On the one hand there were ad hoc formations built around the idea of 'partisan warfare': Grassin's Legion, a unit of 600 light infantry and 300 light cavalry, served through the War of the Austrian Succession and did end up seeing fighting – in skirmish order – at the Battle of Fontenoy; during the Seven Years' War, the Prussians made extensive use of Freikorps formations to carry out a 'small war' of raiding and harassment against their French, Austrian, and Russian adversaries; the British in North America assembled their own comparable forces, most prominently Rogers' Rangers. But there were also more established light forces as well: Prussia assembled its own regular forces of Jäger and Hussars; the British army arguably began using light troops when it assembled its first Highland regiments between 1710 and 1739 (though such forces came to be more 'standard' line troops in time), but it firmly established permanent bodies of these in 1770, when each battalion was required to designate one of its ten companies as light infantry.
Light troops performed two principal roles: supporting the army on campaign, and serving as a more flexible, though less decisive, arm in battle. On campaign, 'partisan' forces attached to armies would conduct reconnaissance, procure supplies if needed, and harass enemy troops and logistics if the opportunity presented itself, as well as attempting to prevent the enemy's light troops doing the same. In battle, light infantry generally lacked the ability to perform decisive shock action, but the approach of individually aimed fire conducted in loose order gave them substantial 'staying power' so to speak, as they peppered enemy troops with fire while limiting the casualties they themselves took, allowing engagements to stretch out. Light cavalry were not perceived as having the same level of shock potential as heavier cavalry, but they could still launch a decent assault on a vulnerable position in the enemy's formations, or run down and scatter a demoralised force.
In short, I simply cannot agree with the premise of the question. The period described – even if we cut out the French Revolutionary and Napoleonic Wars – can be argued to have seen two major shifts take place: one in artillery, primarily up to the 1760s, and one in the use of light troops, primarily from the 1740s onwards, both of which saw a considerable increase in quantity and refinement in quality and usage.