Mid role heroes. Bad idea?

Would more mid role heroes be a bad idea? What i mean is, look at Mr fantastic. Everyone says he is pseudo tank due to his ability to FACE TANK so much damage. This is balanced by his lack of high damage output. Rocket could be another good example. Able to output good damage, has an ult that further increases damage, but is balanced by the lack of burst healing.

I'd love to see a tank that had small amounts of team healing abilities. Some like like penni with her webs, but able to heal everyone standing in them, not just herself.

Maybe this would be hard to balance, I don't know. But I feel like it'd be a great way to shake up the go to 2-2-2 meta. Only one healer? It's cool, a tank and our dps can both do minor healing too!