I think you will receive a wide variety of responses. To be honest, DS 10 is still this way. I think you need to see what works for each child and go with it. If it were a book, how much sit time would be acceptable? DS does not learn from books the way he learns on a screen. I had hoped he would take to books better as he aged, but it has gotten worse. So I made peace with screen time. I monitor pretty severely. If you start to see addictive behavior (different than obsessive), I would reassess.
That's interesting that your son still has an affinity for learning from screens. I also had assumed my son would get more book-oriented as he grows older (and learns to read better). May I ask how one would distinguish addictive vs. obsessive behavior when it comes to screen time?