This has a lot of consequences. Like they willingly get out of bed, get dressed, and eat breakfast so they can have screen time before school. After school it's finish homework, bathe, etc. In our house screen time is basically a given unless they do something to lose it. Sometimes when they argue constantly I'll say "No screen time, you can earn it back when I've heard you each say 5 nice things to the other" or something to that effect.
Our kids are accustomed to this, I've been super consistent since they were little. I do sometimes wonder if there are unforseen side effects that may be detrimental. Otherwise they seem to have done really well. Edit to add; ours don't have phones yet, I'll probably be leaning on iOS parental controls.
The only detrimental effect I can think of is your kids not being accustomed to regulating their own behavior as they grow older (like say, turning 18 and going off to college if you don’t loosen the control before hand). But that is a normal parenting problem.
It's not a subject I'm terribly interested or familiar with, but parenting strategies from a distance sound extremely barbaric
I don't think we can be expected to fight a one-sided race forever. At some point you simply have to block the mind-virus games and websites which have been perfectly tailored to infect young minds.
Discuss boundaries with your kids. Explain why healthy balance of screen time is important. Enable them to take responsibility for their own time. This is a long-term play ;)