All this obsession with learning reading and maths etc early is silly and completely unproven by research to help children do well later in life. Finland is the country at top of PISA, the International comparison table for schools, and the kids there start school much later and have very little homework. It's a bit like walking: just because one child starts to walk later than another, this does not mean they will be less good at walking once they're older. We can all recognise the ridiculousness of thinking this would be the case, but for some reason not when it comes to school.
Of course children need to learn self discipline and to learn that the my can't always just do what they want, and somethings they need to knuckle down, but if you enforce too much pressure too early on, it becomes counterproductive.
Generally, I would say that a lot also depend on the child. Some are very calm and ready to do sit down academic activities, and if your kids are like that, by all means, pile on the homework! As long as they are thriving. But forcing a young child who is not into sit down activities, and who has already had a (imo way too) long day at school, to sit down and do more academic work, will
Only make this child resent school work. Children also learn through play, thy need to be physically active too, and they also need down time - they are developing at break neck speed and their minds and bodies need rest sometimes!
To me it sounds like what you are doing is just the right thing. If you see your kids falling massively behind when they're older, then is the time to start pushing them a bit more, but for now, let the children be children. Children are not mini adults, who respond well to competition and pressure, but small humans who are just beginning to develop and find their way in the world. They need love and support more than anything, not pressure and competition. Look at recent statistics of how many children in this country suffer from stress and depression and ask yourself if that is related to the school system and if that healthy.