I don't get what problem people have with concentration spells at all. It's a key component of balance in 5e and as far as I can tell it's been rather faithfully implemented. If it wasn't casters would be bonkers OP. Yes, that means you have to take steps to defend the casters with stuff like Sentinel, enviromentals, layered spell defense, etc, but that's part of the tactical play. The only thing missing compared to 5e is cover. Not being able to cover for another +2 or +5 to AC, along with high ground archers getting +2 on attack, can mean anywhere from +2 to +9 increased chance to hit. Which is pretty massive tbh.
Given that cover isn't it, ranged attacks REALLY shouldn't get +2 to attack from higher ground, as it isn't part of the rules and skews the likelihood to hit. Archers sniping casters is a pain (melee you should manage) so when a 5e core mod comes around I trust it takes away the silly +2 to ranged attacks from higher ground and allow me to drop prone to impose disadvantage on ranged attack. See, if they just stuck to the 5e rules it would actually just have been MUCH better for the casters defensively speaking. The issue isn't concentration, the issue is deviating from other rules.
I generally avoid Concentration spells because of the issues with the rules. I think a corresponding change to Concentration is merited.
For example, I think you could make Concentrate a Skill instead of a CON save, making it take a little more work to optimize but with bigger payoff. You could then take an Action to "Focus Concentration" to gain Advantage on saves to Maintain Concentration. War Caster could give you Expertise in Concentrate, plus the Shocking Grasp benefit, and you can use Maintain Concentration as a Bonus Action (but you'd still be pretty good without the Concentrate Action because of Expertise). You could do the same thing without making Concentrate a Skill, but it seems like a Proficiency Slot is about what the upgrade is worth (not a whole additional feat). And you could perhaps impose Disadvantage (canceled if you Focus Concentration) if you try to maintain two spells.
