Doesn't matter. The fact of the matter is that Piranha will forever be saddled with the point that no one asked for him. Joke character or not the character is far from a popular choice as a character free or not.
What does matter to people is that instead of resources and development time being put towards a Krystal, or a Geno, or an Isaac, or a Bandanna Dee, or an Ashley, or a Skull Kid; or even echoes like Black Knight, Shadow, or Hilda, they decided to devote time and resources to a character that was merely added for shock value. Now don't get me wrong, I love the idea of Piranha Plant, as a regular little nook of an enemy he kind of fill that little niche. A normal *** normal enemy. And while I'm not overtly frustrated with his inclusion I wholly understand the frustration caused by his inclusion but honestly I do find the idea of shock characters annoying. For instance Akuma and Geese came out to Tekken 7 to worldwide praise for calling back to the legacy of fighting games. Comoare these to a Ridley or a K. Rool. On the other side of the spectrum Noctis got announced and people were confused and baffled by his inclusion. Did he turn out to be a cool character? Absolutely. People love him now. Compare this to a Snake, Cloud, or Simon. And more recently, and most appropriate for an example, Negan from The Walking Dead got announced for the game. There is really no point in adding said character except for shock value. That little boost of hype that can get eyes on the game from a more mainstream audience. Compare this to Piranha Plant. The difference is PP doesn't have the trait of reaching out to further audiences. It's a simple out of the blue character. Would have we lamented Piranha Plant if he never ever got into Smash? Nah. Not at all. Because most of us dont care. He's just a goofy character.
I do think the whole PP announcement was done incredibly poorly, you could even say maybe in bad taste. After months of speculation about Shadow and Isaac the bomb is dropped that they're Assist trophies. Then almost immediately followed up with a character trailer for a LITERAL generic enemy. Not even a discernable trait like Bandanna Dee or Captain Toad. Just a plant. As an Isaac fan I can tell you it was a hell of a blow to see Isaac as an Assist and a Mario Plant as a character.
Though I digress. To answer your question quite simply. Probably. But no. With any of those kore popular or preferred characters they could have sold that first character and people would have jumped on it. The only way they could get away with PP was by making it free. Could you imagine if someone bought the Fighters Pass expecting something special and instead got... plant? Alas, people will complain about anything and everything so on the other side, yeah, people would've complained. Resources could've went to any character I listed above to upgrade them from an Assist but they didn't do that. They decided to make Piranha Plant.
Honestly, I'm fine with PP but if you really REALLY can't see why people are upset by his inclusion over Geno, Isaac, Ashley, etc. then you are wearing some damn thick blinders.
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