An idea is worthless without implementation; the question is, who will implement it, and where will the models and animations come from?
Furthermore, only "cavalry" and "mages" look logical; the other groups are too dissimilar.
If one were to attempt symmetry, it would be based on the types "flying unit (fast) - infantry (slow) - ranged attacker/caster" in a small (levels 1-3) and large (levels 4-6) form, but again, as mentioned above, no one will do this.