If the chant that Bard used before shooting the Black Arrow was magical, does that make Bard magical as well? I would argue that it doesn’t, and therefore Bard is a reasonable representative of a mid-to-high level fighter.
The main point is that it is Bard’s player’s choice as to how magical he is, and whether actions in game are magical. Maybe one Rogue’s Evasion ability is tied to his being a tiefling, tabaxi or a halfling, or having some sort of latent magical ability, or just being that good.
But tagging Evasion with a Ex tag or a Su tag is a solution in search of a problem.