Well, that blows. Maybe it will get invincibility patched in later on like with Falco's Up Smash in Smash 4. I'm not even sure why it doesn't have at least head invincibility in the first place. Wolf's Up Smash low profiling helps, but I don't think it's that powerful where it couldn't have some invincibility.
Wolf's Smashes are different, but he is at a slight disadvantage when Fox and Falco have invincibility on their Smashes. Both of them have invincibility on their Up Smash and Down Smash. Fox had head invincibility since Melee and maybe Ultimate where if it becomes leg invincibility or gains upper body would be pretty helpful while Falco had the same thing until Smash 4 where his bootleg Somersault Shell didn't have any invincibility until 1.1.4 gave him leg invincibility and it lasted from startup to the active frame because Falco reasons. This move had 14 active frames and no gap between them because that's how they wanted his dumb Up Smash to work after 1.0.8. And now he has a bootleg version of Rugal Bernstein's Genocide Cutter because once again, Falco reasons. I swear if it's still invincible for all its active frames again in Ultimate.
Wolf shoots up pretty high and Bowser is going downwards towards him. The other thing and I don't know if this would need to be confirmed whenever we get the ability to see hurtboxes, but for some moves, hurtboxes can be extended which if that is happening for Bowser's Bowser Bomb, then that would be another reason. I can't think of a move off the top of my head that does this in Smash 4, but I know in Street Fighter, some moves have extended hurtboxes which helps for whiff punishing and also hurts if the hurtbox is extended too much and on a weird place or move that you wouldn't expect it to be on.
Edit: Walk speed is up on Kuro's site:
http://kuroganehammer.com/Ultimate/WalkSpeed.
Wolf's walk speed is 1.208, the same as Chrom, Corrin, Roy, and Yoshi's. He actually went down in speed in Ultimate which is odd. His Brawl walk speed was 1.3, so he was like Melee Falco where his run speed was only 0.1 higher than his walk speed. It's still all right, but strange. In a way, Ultimate Wolf traded walk speed for run speed as his run speed went up by 0.14 while his walk speed went down by 0.092. Considering changes to dashing, it's a good trade, but having a fast(er) walk speed would have still been useful.