IMO a better system is what many have already said:
Only allow 1 more of each role than could be choose in normal role queue (2 tanks max, 3dps and 3 heals) and keep the normal MH switching. That leaves room for roles to still move around. Change tank HP from flat decreases to % decreases of max HP (JK barely has more HP than reaper in MH). And ffs stop allowing duplicate characters (I HATE THAT). It isn’t fun going up against multiple, bastions, hogs, moiras…etc.