All of us who have played in patrol zones with Doom's in the zone already know the problem very well
Your melee hero becomes invisible surrounded by a dozen or more summons. No matter how you configure effects or visuals.
Slow computers suffer even more due to the lag.
I throw a suggestion which is just to reduce by 40% (at least) the number of summoned minions and increase the damage of the rest by the same amount.
I don't see many problems to implement this suggestion and all players (even summoners) will enjoy a cleaner battlefield.
Feel free to add more ideas to help solving this issue.