There is nothing wrong with the current holiday system in terms of how children deal with them and their learning, ime and imo.
The short one week ones are good for refreshing the children.
The longer breaks are good for that complete break, and to let families spend time together too.
The long summer break - children can really wind down, have a complete breather, take time to do other stuff, let families holiday, etc.
Independent schools have even longer holidays and cope just fine.
In other countries the schools often have even longer holidays and cope fine.
You know, school is about what is right for the children. They don't need to be there all day every day for every week of the year. They need a balance.
As for if suiting working parents - well, that is a choice you make when you chose to have children really. The holidays are no surprise, they've been like it for a long time now.
This is a childcare issue not a school and children issue. The two are different. Fine - of there is the need for longer childcare - then look at that. But school is not childcare.