There is no "Requirement" to reach 97% or to provide doctors letters
There is a "requirement" for the school to be able to demonstrate to ofsted that they have threatened and cajoled parents into improving attendance
Schools are not "over stepping" - ofsted is ( ie the government)
No body cares, honestly.
I send shirty letters out to parents who have kept their children off school, not because I disagree or disapprove of the reasons, but because I am required to by the government.
Honestly, that is all I have to do - be shirty with you. Once I have done that, job done, forget about it.
What happens if you are taken to court? Nothing, just have your personal records ready to show, thats all.
Fines etc, that happens when people wilfully remove children for term time holidays, etc. And to be honest, even when that has happened, if it is for a good reason, I just do by obligatory "shirty" bit, and move on/ ( sometimes secretly applauding parent for their decisions, and certainly never in any way holding the child responsible)