The thing is, Dark Pit's recovery is much the same yet is considered bad and gimpable at high level because of the lack of a hitbox. And I have gimped Inklings before (though I admit Falco, Shulk and Dark Pit have above average edge guarding, it's probably harder for say Mario), it's far safer than gimping say Ike or especially Wolf. The lack of a hitbox means more than you might think.
Well I didn't say it'd be ungimpable, just that it wouldn't be easy. Not enough to be considered a core weakness of Joker's once his persona comes out. And again, that move also has invincibility which'll really help make up for a lack of a hitbox. The gimp window will probably be pretty tight.
And while those traits are what make Wolf and Peach good, it's the insane damage and knockback that push them into 'broken'.
I guess my point was that it's just more complicated then that. It's not power and knockback that solely make them so strong, it's how their entire kits come together combined with their power. Wolf, for instance, might have some powerful attacks but landing them is kind of tricky, but luckily for him he's got such a strong presence in both neutral and advantage that he can find plenty of opportunities to go for them. His smash attacks and Bair are all quite slow on start up and are only really superior to superheavies in terms of endlag (which does make them much harder to punish, but not any easier to land).
There are a lot of other things we have to know about Joker. Will his frame data be any good relative to his range or will it be just slightly lacking in some areas? Will Gun be effective as a zoning or harassment tool, or will it just be a gimmick? How difficult will charging his persona gauge be, how much stronger will it actually make him, and how necessary will it be to do so? Will he have a clear gameplan or will his approach and zoning both be so undertuned that neither will carry him? There's a lot of things that could go right or wrong here. A mobile character with knife range and a burst mode does sound really good on paper at least, so it's really likely that he'll at least be decent (and more likely that he'll be pretty dang good).
I guess what I'm trying to say is that having power won't guarantee that he's good, and too a lesser extant lacking it a bit won't guarantee that's he's bad either. Inkling lacks power outside of roller and laggy smash attacks but has still mostly likely secured herself a spot in high tier, while Ryu and Ken can both dish out impressive damage but are struggling to see usage because their limited mobility and effort to play just aren't enough to justify their solid reward game.
I personally don't really think either Wolf nor Peach truly broken, by the way. Just maybe a bit overtuned, but that's another discussion.