Zard neutral is kind of bad but it's not unsalvageable, it just revolves around getting reads. I'm not talking hard F-smash reads, I'm talking about knowing what move to approach with or what habit to look out for. Nair to land on opponents and beat out short ranged attacks, grab to beat shield, flamethrower or Bair if they try to wall you out, ect. Running up and shielding to get an Up Smash punish is also really effective, especially since Zard's fantastic ground mobility makes it very easy to mess up your opponent's spacing. This is really effective against sword characters who are dependent on good spacing to wall their opponents out.
His hitboxes really aren't a problem. So what if Up Tilt doesn't hit in front of him? That's not Up Tilt's job - he has a frame 4 jab and frame 6 Usmash for that. U-Tilt is a juggling and platform pressure tool you use when your opponent is above your head, and it's massive disjoint is really useful for that. Fair isn't a very good neutral tool but it's lethal in advantage. Bair is the only hitbox I really take issue with since it feels really hard to consistently land it on grounded opponents sometimes, but when you do it's worth it, especially if you get the tipper.
I don't get what people have against his Nair. It's better then Ivysaur's, imo. It's sort of bad out of shield sure but he's got Up Smash and Fly for that. Meanwhile Nair move frame traps pretty well and true combos into jab. It can be oppressive if you have stage control and your opponent is trying to jump over you, especially if they're trying to escape from the ledge in particular. It's also fantastic juggling tool with Zard's buffed air speed, especially since it can catch air dodges thanks to its large lingering hitbox. It's also a nifty edgeguarding tool for similar reasons.
The nice thing is that you can use Squirtle or Ivysaur to download and/or condition the opponent first, then use Charizard to capitalize on that. That's what I always do. Some matches I hardly use Zard at all, but in other ones I use Squirt and Ivy to safely poke around until I figure out how to use Zard optimally.
People are giving up on Zard far too fast I feel. Maybe my opinion as a crazy loyalist doesn't mean much, but I'm getting a ton of mileage out of him. At the very least, he feels better off then he was in Smash 4.
Edit: And Charizard wasn't just nerfed into Ultimate, he's received some significant buffs as well. The biggest one, imo, being the sizable boost to his air speed. Not only does this improve his approach, but it also makes his already bonkers advantage stage even stronger. It even helps his disadvantage a little. Up Smash now connects consistently, so no more having opponents falling out of it for no good reason. Up Tilt's hitbox is massive now. Flare Blitz is a better kill move then it used to be. Meanwhile the only nerf I feel is kind of significant is Fair no longer autocancles.