Predictably I am the first to answer this.*
I am passionately opposed to homework at primary school. I see no need for it when our children have longer school days then almost anywhere else in the world. So when my children were at primary school (and we did have a brief foray into a private school for various reasons) I made known my opposition to teachers (who all, without exception, agreed with me) and said I would not be supervising homework, encouraging it, nor making space in my children's lives for it. I prioritised play and free time. Now, sometimes my children were very keen to do their homework, so they did. Sometimes they asked for help with it, so I helped them. On several occasions I did it for them (a tip I read from an educational psychologist once), in my own writing and everything - this when they were too tired to do it and at the same time were worried that they might be in trouble - one nasty teacher and one supply teacher. Also during one particular period, the school required children to learn their spellings by writing them out every single day on a form made specially for the purpose. One of my children has a photographic memory for such things so didn't need to do this. I went to the school to ask for DC to be excused but was told that wasn't possible; so I did those myself too. I also did colouring homework as my children all loathed colouring and I see it as an entirely pointless activity but quite enjoyed it now and then. I must stress that my children were never, ever punished for my stance.
Now, all my children are much older - what is their take on this? They say they had a fabulous childhood and say I was very brave and strong to do it. They also say that they were probably much keener to do homework when they got to secondary school as there was a novelty value to it. They are all academic high-achievers but they all work for themselves, not for me. They tease me now about how I stopped them doing their homework and we can all laugh about it.
In answer to the other part of your question, at my sons' grammar school there is very little homework. They do it at school. Now I have one in sixth form there seems to be a fair amount of private study, but no one has ever been burdened with masses of work here. My daughter left school a couple of years ago and again, never got dragged down by masses of work, though she does work hard for herself.
You sound as if you are brilliantly aware of your child's needs and I would urge and encourage you to resist the pressure coming from school to study for hours. It isn't necessary, it doesn't 'get them into the habit' of working and it is entirely possible for them to develop a really good work ethic later on without sitting for hours going over stuff when they are little. Don't let anyone tell you that if they don't develop this ethic at 6 they never will. Your instincts are in my view spot on and you should run with them. You might actually find that teachers (and I was one for a long time) agree with you.
* and predictably you beat me to it by being concise, G55