Honestly I’ve come to expect weak final bosses as the norm, rather than the exception. This year Horizon Zero Dawn and Breath of the Wild come to mind as games that weren’t able to give themselves a satisfying conclusion in gameplay.
Horizon used a a turret sequence followed by a rematch with the least interesting “powerful” machine, the Deathbringer, supported by some basic adds. Zelda’s final boss had a decent first phase, then finished with what felt like an unfinished Divine Beast attack sequence. A final boss doesn’t have to be the hardest part of a video game, but it was completely at odds with the world-ending powers that the preceding cutscene promises.
Looking at last year it wasn’t so hot either. Doom, Banner Saga 2, Hyper Light Drifter, Uncharted 4, and Dark Souls III all had final bosses that felt like they missed the mark. In most cases, it wasn’t because the fights were badly designed or easy, but more to do with how the game had not given them adequate buildup. Being surprised that something was the final fight is never a good thing.