And since everyone gets to disengage as a bonus action in this game it's pretty impossible to make a mob stick to your tank.
People keep saying this, I've seen this over and over. The Disengage change, so far, has no effect on the AI enemies. They don't Disengage, except for Goblins, who already had that as a racial ability even in pen-and-paper 5e. Nothing else really Disengages. My melee characters get attacks of opportunity all the time.