I don't mind the enemy moving around their melee opponent. What I have a problem with is the fact they get backstab bonuses. This shouldn't be the case because the enemy is aware of your presence and it's not because you disappear from where they are facing that you are not here anymore.
The other issue, more serious, that I have is disengage being a bonus action. It should be a full action and nobody should be able to attack the same turn they disengage.
