I wish they knew both more and less, depending. No paradox just a synthesis per the Hegelian dialectic. I've seen ads which were clearly leveraging a creepy/dangerous piece of info they had about me. And I've seen dumb ads trying to sell me products I no longer have any reasonable interest in because I just fricken bought them the damn thing.

The advertising ecosystem is bad and broken in both directions within the dimensions of what they know, how much they know and in how they leverage it.