Most powerful race? Pretender?

[Taqwus]

It really, really depends.

For instance, in a large map with at least normal research speed and maximum magic site frequency, the sheer amount of magic resources and the likelihood of plentiful research before the game is over will favor magic over even the better mundane troop types.

Even a prot-30 vampire queen with all elemental immunities is going to die pretty quick if smacked around by a Niefel Jarl with quickness and a gate cleaver (armor negating magic toy with 29 base damage; will badly hurt most things quite quickly, and it's not even unique). Anything falls unconscious if hit by Magebane; hit twice and it can basically forget about waking up for the rest of the battle (100 fatigue per hit).