Types don't matter at all in Smash, though, aside from when we had PT and each starter had a weakness IIRC. You already mentioned it but Melee had two electric types, Pikachu and Pichu. That disproves the point that we can't have Pokemon of a similar type in Smash. Saying that Squirtle can't be in he's water and Greninja is water is like saying we can't have Rex or Elma or Takamaru or whoever else because they use a sword and we already have over characters who already use swords. Even if they're both Water type, Greninja and Squirtle obviously fight differently, just like how all of our sword wielders fight differently.
And yeah I explained my last part about a veteran being a new character horribly, I meant that they're still work to add in, similar to adding a new character, so that's why I said "10 new characters" instead of "6 newcomers, 4 vets". I wouldn't call Squirt/Ivysaur high priority characters but we aren't Sakurai so neither of our comments on their priority have a basis
yeah veterans aren't "newcomers" or new characters, but I think that they can almost be considered one in terms of workload, that's what I was trying to say. I just did it horribly
since veterans are still an addition to the roster that has to be balanced just like a newcomer, they have to have their models updated, etc. But I know nothing of game design so I'm probably still wrong on this point