On the flip side, I've survived a lot of Zero Suit ladder combos with Zard that would have killed almost any other fighter.
You might have survived a Zamus ladder like 5-10% longer, but then also died to many ladders you simply wouldn't have gotten hit by as another character, I know I've died countless times as Zard and ROB to ladders that wouldn't have worked on me as most other characters.
Well, that's exactly how it is Pokémon. You're still in a 1v1 setting, and if your single Charizard is your only strong suit while the rest of your team isn't on the same level to help balance out your matchups, you're still going to get steamrolled once he's down, especially against someone who has better matchups against you. Like I said, you can try to power through against a team, and it might work, but you're at a bigger detriment than having a well composed team.
No Pokemon is not comparable here, in Pokemon your team isn't sharing a health bar, and in Smash there is no "rest of the team" for your opponent, you're just fighting that same overlevelled Charizard for every stock, and you're opponent is never obligated to switch to a character they're not practiced (i.e. "levelled" for this analogy) with between games. You take his stock (e.g. knock him out), that same character (or Pokemon in this analogy) comes right back out, there is no anemic "rest of the team" to fight instead, and matchup advantages don't matter if you're not near his level, which is going to be much harder to do if you're juggling much more characters around.
Same with old Marvel games like MvC (Outside of having limited assists), XvSF, and even Marvel Infinite outside of Soul Stone, once your best character got blown back and you weren't up to par with your secondary, you're still going to lose that match. And that can be equated to stocks, as using your weaker character against someone who's more skilled with their selection will cause you to lose one immediately.
Besides the fact they're completely different games, there's one critical flaw in your analogy; using a team of characters in those games is mandatory, while in Smash you're never forced to use any other characters mid-game nor do tournaments force it mid-set in the main singles bracket.
Also, you have to remember health management factors into Smash, especially with PT, alongside being vitally important in Marvel games. Despite showing two separate health bars, it's practically one as you need to keep synergy between your team and have your options open.
Your pokemon share the same damage meter in Smash, they don't have individual damage meters. All you can do is switch to a heavier pokemon to "live longer" or switch to micromanage opposing combo/kill confirm windows in terms of health management.