You could double the health on the heros that are supposed to control the flow of fights and it MIGHT be a start. Seriously, fight pit is a joke as far as PvP is concerned. Nobody gets to do anything. Blink and it's over. Coliseum might have one interesting fight out of the 3.
PvM ... I really miss when we tried to kill the Boss Pits. Wish you could implement some weekly randomness like War Mods to make them a challenge or require thought. Maybe bonus loot for using certain neglected heros or something.
There is something about watching your pre chosen 5 heroes work in coordination over the course of ninety seconds that has been utterly lost over the last year. All the focus is on synergy of buffs and debuffs that occur instantly or passively. Due to massive damage, heroes fully charged to the battle, or energy being drained/heroes shut down so they have no effect. It's given us little choice to be creative.