I don't find it strange or problematic that FE has no villain rep. The series has like 20 characters who could feasibly be called a "main protagonist," and they're more diverse than many people give them credit for.
Late on this, but this is essentially where I'm at as well.
Like, contrary to what a lot of people seem to think, the main lords of each game tend to be those games' most popular characters. As well, often times the villains are among each game's
least popular characters, at least for the main villains. To allocate a slot specifically for a Fire Emblem villain, they'd not only need to be feasibly chosen over or alongside the game's more popular protagonist, but also be popular enough in their
own right to warrant.
Black Knight, Arvis, Edelgard if you count her despite her also being a protagonist, and Veronica if you want to stretch the villain definition to Meta Knight levels of "yeah I guess you were an antagonist once" are pretty much the only Fire Emblem antagonists to even be able to do this. I'd count Rhea as well, but there's zero chance they'd ever go for her over one of the House Leaders, and
especially not before Edelgard.
And even then they come with their own issues. Black Knight would need to be justified as having over Micaiah, who is more popular
and a main protagonist. Arvis would need to be justified over both Sigurd and Seliph (which may be done through the complications of fighting on horseback), but would also need to be justified over Julia, who gets a lot of love from IS. Veronica would also need to be justified over Alfonse and Sharena, who are also popular in their own right. Edelgard would rely on them picking a second Three Houses character in, presumably, a post-Engage world.
It says a lot when most of the actually popular
side characters, never mind main characters, have been playable in Fire Emblem Heroes for years, when on the main villain side, folks like Jedah, Raydrik, Nergal, Validar, Anankos, and Thales are still MIA when Heroes is about to celebrate its sixth anniversary next month.