If you do what you’re talking about, you wouldn’t even have Heroic raid.
I’ve played MMOs that don’t have structured class roles. Hell, I even enjoy Monster Hunter. But the multiplayer in those games still just boil down to other people playing a single-player game at the same time as you with little way to support each other as a party. At best, one of them is temporarily bait and runs around in circles for a bit because they don’t have any way to be bait effectively.