Then it turns out you're not really much good with Squirtle and Ivysaur, so switching to them doesn't actually help and if anything makes it harder to win, and that by trying to force yourself to play all three you're spreading your development time thinner across three wildly different characters that are very unlikely to all be fitting for you, making you develop more slowly with them while that time could have been put to a different group of characters that actually fit you.
This isn't directed towards you but towards the overhyping I've been seeing Pokemon Trainer get everywhere; I think people are really getting ahead of themselves when they think the Pokemon Trainer is going to be a busted character and act like actually using them as a team is going to be optimal, when you can play the counterpicking game anyway with any character you want and trying to force the individual mons to designated roles (e.g. use Zard for killing!) doesn't work well at all in such a dynamic game like Smash. A big part of why PT failed so hard in Brawl wasn't just because of Stamina or how bad Ivysaur was, but rather how impractical the whole using them as a team was; if Stamina didn't exist in Brawl there would have been a lot more PT players, but 90+% of them would have just focused on Squirtle, with a few low tier heroes focusing on Zard or Ivy, and then a fraction actually trying to use them all as a team. I'm certain after the first few months almost everyone who seriously plays PT is going to focus on a single mon or drop them altogether, regardless of how good each of the pokemon are.
In theory if you're at a near-equivalent high level with all three of the mons and no single character beats them all, then you'll be impervious to paper level matchup-based counterpicking, but the chance of a player clicking with all three and being really good with all of them is pretty damn small, and matchups are only really relevant if the players' characters are near-equivalent in skill levels unless the matchups are extremely lopsided, so that weak Squirtle is still going to get destroyed by that well-practiced Zero Suit Samus that was wrecking your Zard. Then there's being able to use Pokemon Change as a makeshift air dodge, but that has the tremendous con of switching you to a worse character (as you should be using the character you're best with for the matchup to begin with).
The only real benefit I see from being a part of the Pokemon Trainer team is for Ivysaur players being able to change to Zard during recovery as a last ditch recovery attempt to survive what would have been an extremely unlikely/impossible recovery, much like how Sheik players transform into Zelda in Melee to take advantage of her longer recovery when they absolutely need it (and like them then having the trouble of being able to safely get back to the preferred character while being in disadvantage). Overall as a Zard player in Smash 4, I would have much preferred keeping him solo and having an actual down special, but I understand why he was tied back to the PT for the "Everyone is Here!" thing, and Rock Smash wasn't essential so he can still be usable if the rest of him is buffed sufficiently.
The only games I've played with ROB in them are Mario Kart and Smash, but I didn't consider that enough to justify not crossing him out.
