Even in mmos mobs tend to attack high DPS dealers if tank doesn't do his job or aggro is somehow broken.
Yeah, that's true. 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. I see it as a good thing. It makes CC and tactics important. The best tank in D&D isn't even a fighter. It's a totem or ancestral barbarian. At high levels a wolf totem barbarian imposes disadvantage on all attacks against party members within 5ft, which makes mobs REALLY annoyed and focus on the barbarian. Combined with their high health pools and damage resistance, they're way better tanks than fighters, who actually excel at dealing damage thanks for sharpshooter/great weapon master eldrich knights doing 9 attacks in one turn.