Neither of mine went to school before statutory education age. My son developed so much in the months between turning 5 and starting school 3 months later, it would have been a disaster a year earlier, but he could read to a certain extent, he could write on a computer [a BBC which was the sort used in schools] and was a proper little scientist/engineer, you have to consider the child, my daughter started shortly after her 5th birthday, she could have started 4 months earlier, but she did lots of activities, swam, danced,gym, playgroup including for rising school children as well as things round the house and round about. I think that did her more good than an extra term at school, to be honest.
Nurseries etc are in loco parentis, a parent who works can't easily spend time potty training and succeed unless the nursery/childminder helps if potty training is started too early. My daughter managed to potty train herself at just over 2 and was dry at night a couple of years before her brother, he was just over 3 and it just took a couple of days and lots of carrying a potty around and a parent who kept an eye on what was going on, did he start the wee dance, if a nursery has insufficient staff to help a child like him succeed for sure it's not the parents' fault. It's like potty training a dog, when it's happening you need to keep a close eye on them and give them lots of opportunities to succeed, and listen to them when they tell you they need to go.
Let's face it there are adults who can't listen or follow simple instructions; children are all different and reach different milestones at different times. Some children have hearing difficulties, some need extra help, some are autistic, and prefer to play on their own and need help with other things too. Fine motor skills develop at different times too. I'd hope that nowadays more children would be able to feed themself as more parents use baby-led weaning when introducing solids. I wonder if they are counting a lot of children who come from a culture which does not routinely use knives and forks,
Enough talking with children and reading to children should show up any difficulties with speech, but again if a child is at nursery all week, are there enough staff to actually converse with children and read to them.
If children have difficulties it is far better that schools find out and help them than what I know happened in the past, quiet children often got left behind as others got the attention. Given the opportunity at a good school children learn new languages, if they have arrived from another country and speak a different language at home, if some schools can help children do that others can help children who have English as a first language
From what I hear there is not enough play based learning, and too much homework from a young age