Honestly, I think
![Charizard :4charizard: :4charizard:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
is pretty underrated. Sure, he's not exactly top-tier material, but he's definitely better than Dedede in neutral because of his quick aerials and powerful moves. Sure, he's heavy; but then again Zard excels at keeping his foes up close and in range of his attacks. His only glaring flaws are the landing lag on his aerials and maybe his weight and recovery; and custom moves definitely help his recovery. He's absolutely a mid-tier character, not among the likes of Zelda and Default!Palutena.
![Stick Out Tongue :p :p](/styles/default/xenforo/smilies/tongue.gif)
Bengal's 'Zard is proof of how good Charizard can be.
He's pretty quick on the ground. His jabs are great and his tilts are quite good. His NAir is honestly one of the best for a heavy; it's quick and reliable for neutral and also lets you set up for other aerials. FAir is great for edgeguarding and does good damage for it's speed. BAir is great at stagespikes and edgeguarding and DAir is one of the fastest spikes in the game and is reliable to work with. His grab is great OOS and it's quick even when using the standing grab. He has both a combo throw (D-Throw)
and a kill throw (U-Throw), too.
Neutral Special is a good spacing tool and can rack up damage quite well, Up Special is a great kill move and can be set up in multiple ways, Side Special is one of the strongest specials in the game in terms of raw power and can also is a great shield break option, and with Dragon Rush you get not only a good combo tool but also a boost to your recovery and survivability since DR doesn't cause self-damage like Flare Blitz does, meaning using it multiple times has no drawbacks. Down Special is good at shield pressure and also gives you super armor, which is pretty great.
Charizard is by no means a bad character; in fact, he's honestly one of the best heavies in the game. He does have some trouble with characters like Shiek and ZSS, but those are at worst 30/50 in their favor, not total domination. Zard is underused and so his meta isn't developing, thus why people see him as underwhelming.