Why?! That makes no sense... Plus, the Charisma bonus is from an invocation, not the spell itself.
Also, too much OA spamming slows down the game. Too many reactions and interrupt are often cited as why D&D 4e was such a problem.
I think it'd be better to make melee more worthwhile.
I think if you reintroduce marking, making it much harder for someone to ignore the melee characters, then melee becomes valuable as a 'wall'. Then it doesn't really matter if melee or range inflicts more damage, what's important is that the melee character keeps the enemy off of the damage dealer so they can do their job.