Yoshi's are far from the worst
Ike's are prett bad, and more situational, IC's are kinda meh, Ganon and Falcon are bad,Mario's suck too. Suirtle almost has no use in his b attacks, GaW are also meh
Ike, I dunno, the fact that a lot of his specials have super armor should be boosting him. I mean, come on, he can tank something like Zelda's reapperance box and just kill her with Eruption, and same goes for pretty much anyone else with Up Bs that only protect with a small attack. The rest can be Countered. Aether is... well, Aether, and Quick Draw is great for opening an approach -> jab
ICs Up B sweetspots the ledge, so that should account for something, right? Squall Hammer seems to do great for damage and helps Popo recover on his own. The little ice blocks (sorry, I don't even know the name of all of these) can be pretty annoying for people with subpar approaching games in the first place. I've been on the other end of it, and I don't think they're really too horrible. SH that down B and you can rack up nice damage and frustrate your opponent. I suppose they are "meh", but they're not situational.
Ganon and Falcon aren't much better than Yoshi when it comes to B moves. You might have me there, though that Murder Choke sets up way better than Egg Lay. It seems that their Up Bs were improved mainly for recovery purposes, but I guess they're not really much otherwise. Down B is good at closing the gap between opponents, and I think if you use it at a close range distance, it should keep you safe as you'll fly past them. Ganon's spikes near the start of it and it kills pretty early on grounded opponents. I can't say much for C. Falcon as I don't use him. The neutral B moves... eh, I guess that's a mindgame thing. I still can't see what makes them any worse than Yoshi's. I don't know anyone who uses Egg Lay, and Yoshi's down B doesn't seem to get near as much use as any of Falcon/Ganon's moves, not even the neutral B. It's also as easily telegraphed as the other two's down B, but it takes it a step further and goes straight down, all the time. You can at least work with the start-up of the kicks.
Mario's are much better than Yoshi's, imo. That cape alone should place Mario even with Yoshi. Recovery, reflecting, mindgames, gimping, etc. It's a great move all around. FLUDD is great for adding onto Mario's gimp game. It can screw with so many character's recoveries (or at least push them back far enough so they have to grab the ledge if they want to make it back, which means Mario can edgehog). Fireballs are your typical annoyers. The Up B... eh, it's just there to recover, I guess.
Squirtle's are possibly worse than Yoshi's, but it depends on how you look at the Down B. Nevertheless, you win here.
G&W's Up B is amazing. He doesn't enter freefall from it, it has invincibility at the start-up, it slows his falling, etc. There really isn't anything wrong with that move. Sausages limit approaching options, if only a tad bit. The bucket, just by existing, helps to limit long-range projectile spam from some characters, and the attack itself... come on, d-throw -> down B on a failed tech for -1 stock. Judgment is fickle, but the rest make up for it.
I say you've got me for sure on Squirtle, and Ganon/C. Falcon are possibly even, but the rest I disagree with still.
J/K