It's particularly bad when a final boss is reduced to little more than (or entirely of) QTE's, when the game's core gameplay was not.
A few games off the top of my head that have QTE final bosses:
The key to a satisfying final boss is that it should require the summation of skills (both as a player and your character) that you've accumulated up to that point. Or at the very least, some semblance of the gameplay you've enjoyed enough to get that far in the first place.
A QTE final boss makes it feel like all the practice and thought you've put into the gameplay up to that point was for nothing. Your adaptation to the control scheme, understanding of the core mechanics, careful allocation of skill points, development of personal style, and good old fashioned muscle memory. All of that is rendered void and now all you get is an interactive cutscene that disregards the time and effort you've put into the game.
I don't mind if the FINAL blow is a QTE if it's particularly fancy and couldn't have been done through the basic controls. However, there should still be a proper battle leading up to that point, so it still feels like your skills matter.