Since we only have proof he was considering Blastoise, I wonder if he always thought Venusaur wouldn't work as well as Ivysaur?
It's either that or it was "the last choice" type of thing. Ivysaur might've been a last minute thing, due to the middle stage factor. He might've considered Bulbasaur too due to the Anime prominence, which is probably why Squirtle was on his mind as well as the fact that Squirtle moves at a higher speed, creating a strong balance. Besides, Ivysaur could be switched with Bulbasaur and Squirtle with Wartortle for the same effect due to pretty much the same bodyshape. The anime probably influenced which of the two previous forms. Not cause Ash(Red's counterpart) used it, but more due to it being way more active than Wartortle who is barely used. It doesn't help that all three middle forms barely show up, with the first and last forms being rather popular. Charmander is the only first form who doesn't get that much screentime. Ironically Ivysaur is the least used of the middle stages too.
The quote said "there's no way they would add 2 pokemon from the same generation into smash".
Since it could be interpreted both ways, I put both, an example of two pokemon of the same gen being added in the same game and an example of pokemon of the same gen being added in a later game. Not saying, it will happen. I am saying that it has happened.
Right. I'm just saying that there was reasons for Jigglypuff that don't apply to PT.
However, it is worth noting they were all added(except Mewtwo?) at the time the latest games had them relevant/from the latest game(more or less). Mewtwo is an oddball because the latest games weren't ones where it was a big deal(Gold/Silver/Crystal), making it the only one where the movie is a factor. And you could argue it being the same as Gen 1's design in Gen 2 is close enough to "relevant"(by that, Mewtwo's story in the games was fairly barebones in Gen 1 and 2, so the difference is barely there). Some were added before the games released to the development(Lucario, Greninja, Incineroar), and others not long after(...Everybody else but Mewtwo, really). So basically, bar one Pokemon, right time and place.
PT only really had the remakes release at the right time. But in reality, that's a coincidence. However, now that Sakurai is looking more at the "right time and place" again for Pokemon, someone from the latest game sounds a lot more likely than just returning to a previous repped Generational Pokemon alone. Decidueye was already considered, but more importantly, is in an upcoming game, making it a prime choice. On the other hand, Nintendo is the one choosing the Pokemon, so it doesn't really matter if Sakurai considered the character or not. So who knows what they'll suggest. Gen 8 is still the currently active Gen, then you got other games like Legends Arceus to look at, as well as New Pokemon Snap. There's not a lack of choice.
I hope that explains what I mean here. Bad fanrule, but there's something to be noted for why it is, cause the pattern isn't actually "1 pokemon per gen" anyway.