I think OP is specifically referring to the first time you fight the final boss, it can be pretty disappointing if it turns out to be a cakewalk, but also demoralizing to lose while being so close to the end.
Personally I would rather either:
>Get absolutely destroyed, multiple times even, before actually getting my shit together. Thus rightfully earning the boss's title as the greatest opponent
or
>Struggle and barely manage to come out on top, winning mostly thanks to accumulated experience from previous fights in the game, plus a bit (or a lot) of luck.
Still, it really does depend a lot on the type of game and what the context is to the fight, if there's any at all.