It seems to me that we may still be grappling with the question of "combat fatigue" without a shared definition of what is meant. If Rory's original quotation is the starting point for this period I wonder if you are both really writing of the same thing.
"'The effect of being frequently brought into contact with death, at once wearies and appals the mind of the stoutest soldier. It is a fact, well noted by ancient no less than modern commanders, that, after long and arduous service, the veteran shrinks with disgust from the repetition of the sanguinary work, as if cloyed with destruction, - whereas the soldiers, younger in point of service, rush readily and even gaily into the battle.*'"
The sense I have from this is a "fatigue" related to the experience of death and destruction related pretty directly to "combat" or "battle".
Many of the instances you cite seem to me engendered by a kind of "campaign fatigue," if such a distinction might be made. For instance, after arrival in the Peninsula in June 1809, the 1st Battalion of the 95th doesn't go home for five years! For the vast majority, there is no leave, no rotation, no chance to see family and friends, no R&R, no return to the familiarity of home, no vacation (not even a return to barracks ut cantonments at best), just pretty relentless campaigning, month after month, year after year, in a largely poor and destitute area with few amenities. This must have been the source of some considerable, if subtle, stress that might understandably have shortened the tempers and general enthusiasm of many individuals.
But I am not sure that I see it as having significantly impaired combat efficiency of units [forgive me, but I've only just restarted reading a very interesting history of the Rifles, so maybe I'm about to find out differently :o)]. Quite the contrary: there's Wellington in argument with London trying NOT to let shrunken veteran battalions go home to recruit, but instead putting them together in jury-rigged provisional battalions in order to try to retain their veteran services as long as possible! This from a man who apparently is quite willing to get rid of incompetents at the first opportunity of having replacements. On the face of it, it doesn't seem that Wellington found the services of veteran troops to be diminished, in the main, but rather that their long-experience was something to be profited from.
Perhaps I draw a false distinction between "combat" and "campaign" --forgive me, but then I can only plead the absence of a definition of the terms other than that in Rory's first quotation.
Most interested - Howie