Meanwhile literally every actual Black Knight fan I know when people bafflingly suggest that he can be an Ike echo.
The amount of Frankensteining you'd need to do and clipping issues you'd need to ignore in order for Black Knight to be an Ike echo would make Ganondorf and Dark Samus look Steve-levels of accurate by comparison. You keep acting like "Well it's echo or nothing" is some sort of gotcha when...it's not. It's not one at all. Literally every Black Knight fan I know is
more than happy about him being an Assist Trophy, where he's accurately represented, sufficiently menacing, and given the respect he should have.
And even beyond that...Black Knight is far, FAR from the most requested Fire Emblem character anyway. Even
just within the Tellius games he competes with Micaiah, who is demonstrably more popular both in a Smash sense and a Fire Emblem sense. And that's ignoring the numerous other Fire Emblem characters that are more requested from
outside of Tellius. Lyn, Hector, Edelgard, Dimitri, Claude, and Alear all have significantly more support at this point. Hell, I'd argue that it's possible that
Veronica does, and that Celica still has enough of her support from the heyday of SoV's relevance to eclipse him as well. And, again, Micaiah exists. So you'd be "appeasing" a fanbase that's pretty far down the line by giving them a bastardization of their character that they weren't even asking for.
It's like saying Nabbit should get in as a Bowser Jr. echo because he's never getting in otherwise. Meanwhile, yeah, people tend to like Nabbit...but he's also nowhere near the most popular character in his series when folks like Waluigi, Captain Toad, Geno, Pauline, or even the likes of King Boo or Birdo exist. So shoehorning him in as an echo in a way where he wouldn't even work, all to appease the three people who'd be fine with that, is the epitome of fitting a square peg into a round hole.