Haven't seen the series and have only read one book (Sharpe's Tiger), which I found a great read and hard to put down. For a historical fiction I thought it really did try to ground itself in historical fact even if it had a bit of "re-enactorism" in it. Anyways on to the topic at hand.

Well, let's look at how officers got their positions. My studies have been mostly 18th century but this does apply to early 19th century as well. Officers usually got their positions from commissions, meaning they bought their ranks, or they recruited enough from their region to create at least a platoon. I say usually because the chance of climbing up the ranks did happen, albeit an extremely rare case in the British army. Officers came from landed gentry and nobility with the very few that rose from the ranks. An odd case would be Banastre Tarleton who came from a merchant class, bought his commission as an ensign or cornet officer, and then proceeded to rise up to Lt. Colonel without buying other commissions. Often familial ties within regiments helped with gaining a position in the army. The costs to purchase a commission was no small feat. For example, buying an ensign position, the lowest commissioned officer, had a cost of 200 pounds in a regular infantry regiment. The cost of an ensign position went up with the prestige of a regiment, so an ensign commission would cost 400 pounds and one in the cavalry would cost 1000 pounds. To put into perspective: 200 pounds in 1719 had a cost of 43,700 USD in today's currency; 1000 pounds had a cost of 213K USK. This is of course with inflation and I will post the calculator I used at the bottom. Again, this commission was for the lowest of the officer positions. You could only purchase up to a Colonel position which had a 6000 pound price tag in the regular infantry and a 9000 pound in the cavalry.

Officers did not think highly of their soldiers in the ranks. They described them as oafish, drunks, irresponsible, and scum of society who occasionally showed courage in battle. Most of the common redcoat soldier came from a humble occupation such as laborer, shoemaker, tailor, etc. They had different motives for joining the military than the officer, often economical than social since even society saw the soldier position as a low caste and unpopular. So here in lies the disparity between the ranks.

Much like today, officers did not fraternized with the lower ranks. The NCOs would be the lowest they would regularly talk to, which often consisted of disciplining soldiers or another routine duty. Even if the officer came from the ranks, his superiors would see it as ungentlemanly and unbecoming of his rank to do so. In the 1750s, Lt. Col. Samuel Bever placed Capt. Mathew West under arrest for his inappropriate behavior such as participating in 'shamefull bestialities with some infamous Women in company with, and in presence of many of the private Soldier.' This is not to say that officers did not have any compassion or care for their soldiers. Major John Small of the 84th Royal Highland Regiment wrote a letter to Captain Alexander MacDonald to reduce the sentence of Farquhar McQuarrie, a deserter who Alexander sought to administer corporal punishment: either to be hanged or shot. Small wanted to protect the morale of his troops, or likely the dignity of his regiment, and pushed for leniency. Out of 140 crimes attributed within the 84th, only 14 punishments occurred: 1 execution, and 13 floggings.

Sources: Stephen Brumwell Redcoats: The British Soldier and War in the Americas, 1755-1763

Matthew Dziennik The Fatal Land: War, Empire and the Highland Soldier in British America

Sylvia Frey The British Soldier in America: A Social History of Military Life in the Revolutionary Period

Currency calculator

A good perspective on this question was perhaps Robert Blakeney's. An Irishman enlisted at 15, he served through the Peninsular War and at Walcheren as a Lieutenant and then Captain , mostly of the 28th Light Foot. As such he had to both deal with the high and mighty commanders, and the rank-and-file. He had a high opinion of the leadership of most of his British commanders: Paget, Wellington, Sir John Moore, and Graham get good marks. He has low opinions of the Spanish generals, especially La Pena. He often has a quite low opinion of the soldiers: though always giving them credit for bravery and the ability to fight ( assaulting Badajoz, for example) and for the general performance of his regiment, he also noted their willingness to loot and drink themselves senseless whenever given the chance, even when in a forced retreat with the French at their heels. He indicates there were some useless officers: he notes that from 1808-1813 a good number of them collected at Belem who had little to do and little interest in getting killed. Being exposed to fire and injury was a part of an officer's job, and he certainly does not hide his contempt for them. But of course, if they were avoiding that, they were also not in the field.

He was perfectly willing to be critical of tactics and strategy and idiocy, but when wrote his memoir A Boy in the Peninsular Campaign he was hoping to make a case for getting a promotion to major and some kind of compensation for the smashed leg he suffered in his service. As some of the superior officers involved in his campaign were still alive, it's hard to imagine he would want to hinder his chances by any hard words towards them. Still, you do not get impression that he thought even his fellow lieutenants and captains ( who couldn't do anything for his pension) were the bungling idiots that you see in Sharpe. It's not my field, but I would suspect that Cornwell is pushing the class differences for effect; "lions led by donkeys" is an appealing theme.

Follow up question, if this reputation was well deserved, how much would it have been attributed to the purchase of commissions for officers? Did this problem start to resolve itself after the practice was abandoned?