I think of social media as the fast food of the information landscape. It’s okay to have it a time or two a week but if it’s your entire information and entertainment “diet”, you’re going to feel sick.
Our brains aren’t designed to be lit up with dopamine every 5 seconds for hours on end nor are they designed for foods that are high in sugars, fats, and salts every day.
Even suggesting that computers will replace human brains brings up a moral and ethical question. If the computer is just as smart as a person, then we need to potentially consider that the computer has rights.
As far as AI conquering the world. It needs a "killer app". I don't think we'll really see that until AR glasses that happen to include AI. If it can have context about your day, take action on your behalf, and have the same battery life as a smartphone...