I think we are talking about something that varies by armour type -- an SCA set of armour is indeed more difficult to put on, especially unpracticed, than a quillen + leather or ring mail shirt + helmet. But... scale, field plate, or even simple chainmail really requires two people and a good bit of time to take off or put on. And we aren't talking about jousing armour, here - even well balanced "easy" armour is very heavy. In my present condition (reasonably healthy if sedintary modern male) I would be hard pressed to slap o an outfit that is over half again my body weight, let alone do it quickly.
Then again, I a. don't have a squire, b. didn't grow up wearing even heavier mock training armour to accustm myself, and c. didn't have someone train me.
There was a great documentary last year on BBC America, I think, where a current UK policeman and ?soldier? faced off in a middle ages duel. They were young, sprightly, fit lads in their late 20's early 30's, and they took forever to put on the armour with expert help, and could not sustain the duel - too exhausted from just wearing it!