This is a major pet peeve of mine--final bosses whose difficulty is not even remotely in the same ball park as the rest of the game.
I get wanting to make the final the hardest. I even get if you wanna make it a bit above the logical extrapolation of the difficulty curve.
But for crapping out loud, the
last
thing I wanna do is have the game's pacing come to a screeching halt at exactly the moment everything is coming to a head in terms of drama, and I've gotten used to the curve enough to tell myself "yay I'm gonna finish tonight." I don't wanna ragequit and come back in four months, ragequit again and come back in a year and watch an ending full of characters I don't recognize anymore doing things I don't know the significance of anymore.
If you want the final boss to be stupid hard, that's ok and in fact I am all for it, but you
make the rest of the frickin game hard too
so I'm not completely blindsided by it.
There's a difference between canon and not-stupid.