I won't lie. I would love a Pokemon DLC. Mewtwo is like it.
I get what people mean though by how they want a less used series to get DLC, though. Same with it being possibly an advertising pick.
But I honestly, imo, having no issues if they're an advertisement or not. Cause there's always more to the story. Their moveset relates to part of why they're chosen. It's never been purely for the sake of advertising in any case. Hero? Cause it's the goddamn Hero as is. The first RPG Protagonist on a console. Sure, the exact Hero wasn't used, but the Class concept is massively important. Incineroar/Greninja(I don't count them as being picked for advertising, but eh) were blatantly moveset-related, and noted as why they were particular chosen among other choices. Roy wouldn't have happened if it weren't for last-minute clones. Corrin almost didn't, but Sakurai's team convined him the moveset would be cool. Byleth had the unique moveset mechanic, and Nintendo directly chose the character too(meaning Sakurai had to see potential in them to say yes to using what choices there were).
I've been one for Urshifu, and seeing Pyra/Mythra(who do have similar movesets to a degree, though more unique specials and clearly different properties) made it clear that the idea of a transformation character wouldn't have been an issue, about the only reason I wouldn't consider the Pokemon in question being too likely(at the time I was for them). Nowadays, the only issue is Pokemon SwSh is more or less reaching its limit of "importance" overall, outside of the anime somewhat. So it's not impossible, but as time goes on, I get more doubtful. I don't consider the spirit event damning for the sole fact it only at most hurt a tiny slew of potential choices, and none of the ones specific to the DLC aftergame stuff, which is also important, and the replace for the notable 3rd versions. Something like Resident Evil hit practically every viable choice. Pokemon? There were way more. That, and we know it doesn't have to be the face of a game to get in(Min Min), as there's going to be other circumstances. I'd still think if we get a Pokemon, it'll be something like an advertisement-related one(or at least the core reason it was chosen. As time goes on, it's hard to effectively advertise a game that came out almost a year ago, so).
Either way, I don't see an issue with them. I get where people are coming from, but I welcome fun and unique moveets. I also welcome easy clones and echoes, if it gets a character I like/others like, in. Sure, the echoes can be really bad(...okay, this only applies to Daisy), but they're still a cool concept.