Sure they can do this all at once, but that's three spell slots gone at once. They can be really cool and dominate this encounter, but what about the next?
WIth just level 1 spells without concentration a illusionist with alter reality would break the game.
I do think the designers of 5E went a little overboard applying the concentration mechanic. Some spells are pretty much never going to be taken because they use up your concentration slot. Other spells require you to get into melee, and that's rough because then you get hit and stop concentrating. Then there are completely awesome spells like spiritual weapon that for some bizarre reason don't require concentration. It totally doesn't make any sense to me.
My table finds rolling concentration checks for damage too fiddly for us. So we changed that part, we only make concentration checks when the attack exceeds ac by 5 or more or if the blow bloodied the PC (we kept the concept, I throw a slight penalty on them when they are bloodied, this encourages the players to avoid playing whack a mole, they are less effective if they are low on hp)
It might be more things to track for other tables, but we already do magnitude of success even with attacks, right on ac = half dmg, beat ac by 5 = max dmg, beat ac by 10 = crit, so we are just tying another thing to the magnitude of success
I don't understand the problem. Concentration *is* a fix; the problem was the stacking buffs/debuffs that trivialized the contributions that non-casters made.