Personally, I feel like soldier could be “fixed” by giving him more role specific class loadouts. At the moment the soldier just seems incredibly powerful in ALL ways. Fix that by giving him huge power in certain areas depending on the loadout - AOE Soldier, Disruption Soldier, OMG I have the best gun soldier. I’m sure people could think of more ideas.
Highly diversified class loadouts for the soldier might be interesting though. You could pick which one fits what your team needs, or which fits your play style.