But why are these two still in conversation from multiple people? They've been left by the wayside in terms of marketing AND are one-shots in a series with a fairly consistent main cast. For established franchises, you can have a recurring character left by the wayside OR a one-shot that's been marketed heavily, but NOT a one-shot that's been abandoned.
I don't think they need to receive current marketing for me to think they'd be good additions. A character can have legacy without continuing to be marketed; continued marketing for older and/or one-off characters is just one way that the legacy can be evidenced. Midna and Ghirahim were big characters in their heydays and are still popular and recognized now. I don't think they're likely, but with a more ideal Zelda roster they'd help a lot with representing the series history as a whole, as they come from a pair of landmark console releases that, while having their individual quirks to pick at, did very well from a general audience standpoint. Crucially, they're also highly important characters in their lone mainline appearances, being on-screen consistently with plot-important roles.
Yes, Zelda has a fairly consistent main cast but that main cast consists of only three characters. There are many versions of those three but they are all essentially reincarnations of the same likenesses, and there is just enough unity IMO to pull together a single good moveset to represent each one. But even many people who want multiple Links, Zeldas, and Ganons still want more than just those, too.
I also lower the bar a bit because Zelda is a pretty big, long-running, and successful series, only behind Mario and Pokémon. I'm fine with it having more reps than the other series, and if you consider Zelda characters both recurring and one-off, these two stand out as among the handful of best ones IMO.
Fwiw I also prefer Skull Kid over these two, but I don't think Skull Kid should preclude either of these two.
the Zelda series revolves around the Links and Zeldas' constant battles with Ganon, so it makes sense that they focus exclusively on the main group
I think that's more an argument that they focus primarily, not exclusively, on the core trio; making it completely exclusive I don't think is an effective restriction.
But even still, Midna and Ghirahim are both directly and intensely involved in the Triforce conflict within their respective games, as are other characters like Impa. They still play strongly into that main theme.
On the other hand, there's Fire Emblem which focuses on presenting a new continent or universe almost every game, but there's still the Anna family who appears across different universes. Does ANYONE want Anna to be in Smash?
If Anna was actually important in her roles, then it would absolutely be significant that she recurs, even in a series not focused on making things recur. The better (and, really, less complicated) way to look at Anna is simply that she is always a pretty minor character in the mainline games.
