Question - how are you going to balance heroes, that require working with other heroes?
Take Mercy, for example, and her rez. In highly coordinated environment, 1 rez can make or break fight. In uncoordinated environment, resurrects are mostly useless, due to level of skill of resurrected players not being high enough to make a difference.
Your idea could work, if all heroes were viable on their own, but we have at least 2 whole roles of heroes, that supposed to be viable in combination with someone else.