I arrived to your conclusion just by playing this game, but I can’t stress it enough that the crazy, ridiculous Ults (and some regular abilities) is all around the single worst gameplay element in Overwatch.
I don’t think ALL need to be nerfed, but many do. However I doubt that we will ever see our wish come true as that would remove the accessibility that Blizzard so desperately wants to ensure they reach the widest audience possible. VERY unfortunate considering the rest of the game is so good.