4 things that make an ult character meta
Some sort of disengage tool. The character needs something like joker gun, cloud bair, corrin fair, etc. to be able to to well in-meta. If the character does fight up close, they gotta do a shit ton of damage like Kaz, Luigi or fox
Insane advantage state AND kill power. Character needs to be able to shit out damage and be able to take stocks early.
Usable recovery. Character needs to be able to make it back from far distances and/or be a good edgeguarder
Insane frame data. Having spammable tools with good frame data rly helps. Think of stuff like Steve up tilt, rob down tilt, cloud bair