You are mixing two issues. Expecting school to be a childminding service, eg keeping the dcs just to help the parents or when they are regularly late at pick up etc.
And then you have the issue of schools closing/finishing early ect.
As far as I am concerned, school closing for a PD day is fine, a good thing actually because it means teachers will be on the same wave length, fir example to teach reading and phonics.
School deciding to close an hour early at the end if therm on the other side ... Why? What us the reason for the school to close? What sort of improvement is it going to give to the children to do so?
I have seen other systems working in different countries. Interestingly, countries where most mums are working full time never close early or at the drop of the hat. And the teachers still manage to do whatever needs to be done. On the other side, countries where most mums are SAHM, schools expect parents to be able to just drop everything whenever it suits them 'just for the children'.
In my experience here, the situation is very variable. Some schools seem to think that giving notice is never necessary. That a parent will always be present to pick up whatever the time the school deemed convenient for them. Others are much more careful. Maybe a sign that in a school where most mums work, it us clearly more of an issue so schools have to be more careful?
Eg all our PD days used to be a Monday. But most mums working part time at our school work Mondays and not Fridays. There has been some grumbles from parents and we now have A nice mix of Mondays and Fridays as PD days. Not difficult for the school to do but making things a hell of a lot easier for parents.
In the same way, the very rural school where most children are picked up by bus never finishes earlier it later than usual but the one where most children are walking distance from school and parents pick up think it's ok to have a more 'flexible' approach.
The reality is. The role of a parent should be to take dcs to school on time and pick them up on time. Not to have some flexibility by arriving late or picking up late. (Parents do get some bollocking for that now re absence etc).
On the other side, it sounds fair that the schools aren't foing around with flexible time that cause problems to parents, just as it cause problems to teachers when children arrive late. So no, unless there is a really good reason for it, children should finish at the same time.