I have no idea which part of Ice Climbers' moveset is actually cribbed from a game aside from jumping.
I also don't get why the "They have a Mii Fighter costume" is even an argument Oh no, Mario's hat can be worn by Miis, guess Mario is never coming to Smash bros
I don't feel like the FE characters are good examples for this point, but most of the other characters do demonstrate the point well.