That was just a partial quote. The full explanation went something like this. For context, this is a fourth year Canadian undergraduate class on War in the 18th century, taught by a military historian. Essentially, since it is early in the year, a student asked the professor to explain the reason why soldiers, in say, the American Revolution, marched at each other in lines, seemingly all in futility. He went on briefly to assert the benefits (and yet also noting how this was an oversimplification and not always the case) of this kind of marching; mobility, morale, a line of command, resistance to cavalry charges, the importance of fire density, etc. And then came the quote in question:
"If you ever find yourself wondering why militaries of the past seemingly made use of such stupid tactics and strategies, stop yourself for a minute and remember this: Armies, commanders and soldiers almost always, across continents and millenia, waged war in the most efficient and effective way possible. Innovation was always necessary in war, and chances are they knew something you don't. So if you were to bring a modern military mind back however many years and put them in the same circumstances, with the same terrain, limitation and tools available to them, quickly you would find that not much would have changed. Our ancestors always did the most with what they had."
It isn't verbatim but it's certainly close enough to what he said. He went on to note certain exceptions when it came to religious or cultural aspects outside of battle, such as taking enemy soldiers prisoner or funerary rites (such as in Aztec or Greek war, respectively). Alongside the American Revolution he also noted briefly how some people have the same wrong ideas about warfare in the First World War.
Sorry for the long-winded explanation, I just wanted to get the full idea across. So, does he have a point? Or were there many cases throughout history of entire methods of warfare being based on faulty notions?
Your professor knows what's up. The statement is obviously a simple one, but its succinct. He is essentially warning against hindsight, and like any other type of science, Military science is the result of current generations standing on the shoulders of the previous. Nothing is irrelevant just because it is outmoded in terms of studying military history/science.
We've had question upon question with regard to linear modes of warfare and why it was so dominant; to put it simply it was efficient. All our answers to these questions have hit the points he briefly lists:
He went on briefly to assert the benefits (and yet also noting how this was an oversimplification and not always the case) of this kind of marching; mobility, morale, a line of command, resistance to cavalry charges, the importance of fire density, etc. And then came the quote in question:
Think of it this way, with regards to this quote:
"...Innovation was always necessary in war, and chances are they knew something you don't. So if you were to bring a modern military mind back however many years and put them in the same circumstances, with the same terrain, limitation and tools available to them, quickly you would find that not much would have changed. Our ancestors always did the most with what they had."
There's a reason why places like the RMC, West Point, Saint-Cyr and so on continue to study the campaigns of ancient, classical and early-modern Captains. General Mattis for example ravenously devoured any literature concerning Alexander, yet asides from the most general military principles (such as adapting and innovating) it clearly had little direct impact on the prosecution of his division's offensive.
To answer this:
Or were there many cases throughout history of entire methods of warfare being based on faulty notions?
No, not precisely. Rather, as he noted with the WWI example, there were cases when sound or previously perfected tactics needed to be changed, adapted or discarded with regards to rapidly changing realities in warfare. Small-unit tactics in Infantry units saw a furious scale of expansion in detail and attention in 1915 on part of the French and German militaries. After Napoleon brushed Prussia aside in 1806, a serious and feverous series of councils and reforms were launched by his recovering opponents, such as Austria, to adapt to this new, shifting mode of warfare.
To say that Austrian operations in 1805, or European operations in 1914 were based on faulty notions is a risky thing to conclude, rather its safer and more obvious to say instead they were based on rapidly outmoded forms of warfare.
There are, of course, rare instances where a military simply draws incorrect lessons. Following their defeat in the Solferino campaign of 1859, the Austrians noted the French's willingness to bound battalions forward and engage in swift and short bayonet attacks. They concluded that 'swift and short bayonet attacks' was the thing to emulate, failing to realize that the former was only possible because the French infantry were able to cover and leapfrog due to their rapid-fire rifles. They developed a doctrine known as stosstaktik which was utterly ruinous to their war efforts against the Prussians in 1866. Failing to realize they could not establish fire superiority against the Prussians, they wasted themselves time and again on futile and poorly covered bayonet attacks.
The principle ('a well covered unit may close swiftly for an assault') was sound, but the application ('Can we establish the necessary outbound fire to keep assaulting units safe?') was erroneous.
I agree in part. Your professor's statement is generally correct, provided you recognize that different cultures—and even different individuals—judge efficiency differently. Efficiency refers to the best means to get to a desired end, so both ends and means must be considered, and a quick review of just war theory will review that even within the traditions of Western Civilization, this has been an area of lively debate.
For just two concrete examples, either of which is probably debatable depending on how you understand the period or read the sources, consider Vietnam and the Vikings. In each case, one power, the Franks or the US, thought that winning a war meant holding onto land, and they thought the means of achieving territorial control was winning battles by holding battlefields. So ideas of efficiency guided all levels of warfare, from strategy on down to tactics.
Conversely, their enemies were not as interested in holding land but had human targets. The VC were trying to cow or convince the locals that the South Vietnamese government couldn't protect them and was ineffective, whereas the vikings would raid and pillage for their own purposes without even considering their impacts on Carolingian or Anglo-Saxon legitimacy. In both cases, this meant that raiding was more important than decisive battles, and terrain could almost always be yielded to the enemy without in any way undermining a 'war effort.' So again, ideas about what war should accomplish guided how the combatants designed their strategies, organized their operations, and effected their battlefield tactics.
There's obviously a lot more that goes into it, and the comparison isn't perfect, but the point is that two sides in the same conflict can assess efficiency in wildly different ways. In both cases, cultural ideas impacted the way a conflict was fought and perhaps even constrained the Franks and the US to unwinnable strategies. (Fortunately for the Franks, the vikings later consolidated into kingdoms and changed goals.)
And although I've been speaking in terms of grand strategy, /u/samlir and /u/alriclofgar bring up the concept of honor, which leads us to think about broader ideas of cultural meaning as well. For example, for the Franks, honor meant holding the field, whereas for the vikings, honor meant preserving the life of your chieftain and acquiring loot. So there's lots at stake in your professor's elegant explanation. No, people in the past weren't necessarily stupid or foolish, but it's sometimes hard to understand why they made the decisions that they did.