I worried about my own son playing video games incessantly through his teens and twenties, but now at 28 he has been holding down a stable job for a year and I have got good reports from his employer. He's still a loner IRL though.
Would I worry so much if he were a gym rat or ultramarathoner-- an "exercise addict"? Good question.
Too often people think that because their kid is introverted they shouldn't be alarmed by them not having a social network of any kind. The reality is that there are many many very healthy introverts who still have strong friendships with other people. I'm only saying this because I've seen too often people write off their children's bad lifestyle choices as simply being introverted.
I don't think I got so freaked out by video game addiction until working at my last company where we hired a bunch of people from the gaming industry. They were the ones who told me about how many top-notch behavioral psychologist are employed in the gaming industry to maximize the addictive potential of video games.
We can say what we will about exercise addicts but at least they are getting very healthy bodies and the highly positive mental health benefits of exercise. Plus when you're in a gym or if you are running trail marathons you are going to be doing so with other people who don't sit in there darkened rooms for days on end.
But competing in a lot of ultramarathons isn't necessarily healthy for the long term either. In extreme cases athletes end up with heart muscle scarring and calcification. Somewhat shorter distances might be better. Everything in moderation.