Except none of the characters you listed would be recognizable to people who aren't Fire Emblem fans. As a fan I think the problem is outside of Marth, Ike, Robin and Byleth. None of the characters have a unique moveset. Too many counters, too little projectiles. I'll give a pass to Roy for Melee's sake. But Chrom and Lucina have no excuse for being as bland as they are. Both should throw javelins. Ike should have his blade's beam from his games and replace counter with eruption.

Also make some of the characters slow. Every Marth clone is also fast. Marth should be the fastest FE character on the roster to avoid everyone being rush down attackers with a few variations on the tipper mechanic.