In part of Germany where the cut-off date means that the youngest children in a year are starting school at not quite 6 (cut-off dates vary between states), there was a massive (and successful) campaign by parents to have it put back three months because 'still 5 is too young for them to be starting school'. All over Germany, many many children are deferred for a year (you do have to jump through a couple of hoops but de facto it's parental choice) so in any first year class you may have an age range of 5 and a half (early starting is an option too sometimes) to nearly 8. So the British unease about too-early schooling is not unique.
As PP said, in Germany almost everyone will have been in kindergarten at least 4 hours a day, more usually about 6, from age 3, and many with two working parents from long before that - there is a legal right to a place in subsidised childcare from age 1 (a rather theoretical right in some places atm as provision hasn't kept pace with the law, but it would be exceptionally rare not to have a place by age 3). These are generally run as very consciously 'not-school', so lots of free play, outdoor time, topic-based 'projects' and learning by discovery, and you won't usually find the staff encouraging reading and writing, though in some kindergartens there are some very limited, fun 'classes' around literacy and numeracy in the final year, and if an individual child is interested they won't be stopped. I do think the quite sudden switch to school with sitting at desks, timetabled lessons etc can be quite hard on some children, but they're old enough to navigate it by the time it happens. Usually lessons are mornings only (starting early, but shorter days than the UK in terms of hours) and afternoons are a kind of after-school club (voluntary but low, subsidised income-linked cost) that's a bit of a continuation of the principles of kindergarten but for older children.
Another point is that while kindergarten isn't compulsory, it is pretty universal and a child who's never been in a setting like that will probably really struggle with school. Most SAHPs will send their children to kindergarten for half days from about 3.
I've had all my children here, so never experienced the UK school system as a parent. I think there are things about it that sound lovely, but overall I think the German system gives the better deal to the majority of children, given real life circumstances (which OP seems to be well detached from).