We often hear the argument that children start really young here but, again, that's a misrepresentation. Finland is typically the comparative country used but what most people ignore is that, in Finland, many children are in established pre-schools from the same age and are covering much of the same content. For those that aren't and are at home with parents, there is an expectation that parents will do more with the child and have them ready for the school curriculum. Here, that early learning is covered by schools instead under the guise of "levelling the field" (when really it's about getting parents back into work).
With regards to homework, I'd say that if it's a battle with the child then something, somewhere is going wrong. That may be the specific things the school is setting but it might also be how/when parents are approaching it, their own attitudes towards it, the routines of the house, etc. If that's what a parent is finding as an individual, I'd suggest they speak with the school. They will be able to help, both with what's happening in school but also with what's happening at home. Over the last 12 years I've worked in education, I've seen my schools (and me) do a huge amount with parents on parenting itself, supporting home routines and behaviour management, developing parents' understanding of educational development and even running full literacy and numeracy development classes for the parents who are illiterate or innumerate.
It's worth noting that in countries where children stay at home longer, parenting is absolutely seen as a skill to be learnt and developed, not just something you do. That's why started later can work. Parenting classes and courses are more widely run and very well attended. Here, even suggesting that someone's parenting isn't the "finished product" is seen as insulting and a personal attack.