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.
Pardon me for saying so, but this seems like a very convoluted way to fix something that is much more easily fixed by staying true to the rules. It should be one check when hit, always add con, allow me to drop prone to hide from arrows. A fighter with defensive style, a spear and sentinel + polearm master would then be all the defense a wizard needs. We don't need to invent something new, Larian just needs to do 5e rules justice.
