I never worried too much about limiting screen time. The TV was constantly on in our house when I was growing up and my brother and I were both high academic achievers (IOxford degrees - and he got a doctorate from Cambridge!) despite our working class backgrounds.
And likewise, my daughter, who watched a fair amount of TV when growing up, whenever I thought it would be helpful, or I thought there was something educational on or something she would enjoy - is now a really high academic achiever (and lovely person).
The trouble with research into anything like this, is it's impossible to take our other variables. You can't raise two identical children in two identical families, giving one screen time and the other none.
It makes no sense to me, that these devices which often expose children to new ideas, new vocabulary, new experiences, joyful things like music, drama, dancing, etc etc, are assumed to be so developmentally damaging, and children are assumed to derive more stimulation and growth by playing in some mud.
(Playing in mud is great for kids, or course. But so is music and narrative, etc etc).