I mean, in terms of this logic, we could say one of the cows at Lon Lon Ranch is a character. Or one of the Djinns from Golden Sun. I think I should specify the implied meaning of an "actual" character. An "actual" character is typically unique in both name and appearance. There is only one Super Mario and we all know what he looks like. When I say the name "Geno" there's no ambiguity over who I'm talking about. Shantae, Shadow, Ness, Falco and Megaman are all "actual" characters in that they each have distinct looks, names and personalities. Granted, CHARACTERIZATION can vary as to the depth of said characters but each is iconic in a way far more profound than the hordes of enemies they fight. In the context of generic enemies, however, they have neither individual names, personalities or distinctive features from one to another. They are more of obstacles to the protagonist than actual characters. For example, if I asked someone who their favorite Batman character was, I could guarantee you 1000% that their answer would NEVER be Joker's henchman #3.
And those are all characters in a game in every single case. There is no such thing as "actual" characters. Everybody is a character. That's a large technicality to ignore that every member of a species you come across is a fictional character. It's literally one "being" that counts as a character. They are still individuals. They are non-notable individuals in general, which is a different thing. But what you're mainly describing isn't "actual character" but "notable character".
Let's look at another example: Petey Piranha. Petey Piranha is unique and distinctive. He is MORE of a character than the average piranha plant for these reasons. The fact that nobody even THOUGHT of piranha plant as a viable character prior to its inclusion speaks volumes as to its character compared to the protagonists and villains of our favorite games. Bottom line: PP could be considered a character in the most general of definitions, however, there are a plethora of NAMED, DISTINCTIVE characters out there that would have definitely generated more hype than PP.
So he's a notable character among tons of characters. It's not rocket science in that regard. You don't need to try so hard to dismiss a character. If you don't feel they're notable enough to be playable in Smash, that's fine. But trying to make up silly definitions that go against how game design and writing works is pointless and doesn't actually bolster your point. It's clear that being a character in a game was all that's needed to be playable. I don't know why people think otherwise when we see it plain as day. Also, Piranha Plant is a specific name. So yeah, that's pretty named to begin with. It's a distinctive enough name alone. What, you thought it was anymore special of a name than Pikachu, who is just a species name? Or Villager? Pokemon Trainer?
Characterization is a very small requirement to be in. Having just barely a little is enough. PP doesn't lack it either. Seems pretty full of emotion and doing things in Smash alone, but also is a combination of characters with various personalities wrapped into one. ...Hell, with how many PP various species there are, it looks a lot more notable than Link's bare personality, which is even worse in Smash, as he rarely has emotional responses at all. Determined and being able to scream is... it. Toon Link has a lot more. Young Link is not much better. Smash is pretty known for having some characters that are extremely fat personality-wise.
As we're talking about someone in a work alone, this is the definition that fits Smash in general the most in this context;
"character
A person in a literary work"
There's a lot of definitions, but others can be very similar as basically "Genetics A structure, function, or attribute determined by a gene or a group of genes." Which is more or less a description of a being brought to life at all. You don't need to have majorly defining traits to be a simple character in a game or work. That's just silly. But again, what you want is for Smash to stick with "notable characters", which accurately describes what you're talking about. Generic characters aren't your thing. Though I guess Pokemon is an exception? I never found it one, but eh, to each their own. Either way, I get what you're saying, but you're using a very odd definition of character that makes little sense in Smash. Plus, as noted, PP doesn't lack personality at all, and that's a defining trait A.K.A. Characterization, so it's pretty hard to see how they aren't an actual character in the long run. Not notable enough, sure. I get that. But if personality is the problem, as you're saying heavily... PP isn't the one to look at for a lack of one.