I know it's not exactly the point of the post but I want to go on a tangent and note that it's 100% valid for kids to complain about school even if you have it harder. You should take their feelings seriously because their feelings are just as real to them as you hating your job is to you. When a toddler spills their juice and starts crying, those feelings are just as intense as yours, and you should respond accordingly instead of thinking "don't they know about the wars in the middle east?"
I had an absolutely terrible time in my small underfunded high school due to chronic illness, family tragedy, coming from a poor home, and just generally not having that many friends. I got picked on, I struggled intensely with untreated ADHD and depression, and was just all together miserable.
But to spite all that, I completely understand what people mean when they say they miss that period of their life, and I'd never seek to make them think they're wrong for feeling that. There's a weird defensiveness about this topic where people seem to feel anyone else having any sort of positive association with that period of time somehow invalidates their own hardships.
High School is not a good or bad thing. It's just a thing. An experience that was different for everyone. It's okay to leave it at that.
If you're a social and relatively smart person (or just take the minimum requirements) high school is probably really fun and easy. If you aren't social high school is either a job or a prison.
If you liked high school more than adult life then you probably peaked in high school.
In highschool my average day was 6 hours of school, 1 hour commuting, 5 hours of homework, and then cutting into my sleep to have some brief time to play videogames and argue with people on the internet. It seriously fucked me up.