"SATs a monumental waste of time"
that depends a LOT on how the school approaches them. My DC's school spends exactly the length of the tests (and no prep in advance) in Year 2 - so a total of a few hours. In Year 6 I think they do perhaps 2 sets of mock tests over the year, plus the actual tests on the day - so vcertianly no more than 10 hours over the whole school year.
A maximum of 13 hours over 7 years of schooling.... and I will be honest and say that when looking at schools when we moved I DID look at league tables (for value aded, though, not total scores) as well as Ofsted reports, so I DID use the results of SATs tests to guide school choice. For me, those 13 hours over the 7 years seems proportionate in order to provide a basic level of information about the school in comparison to others.
Obviously if the school followed the bad practice of others and spent many weeks on preparation for SATs, I would agree that is a waste of valuable learning time. So it is not the tests themselves, but the decision of some schools to spend too much time in preparation for the tests, which is the waste of time... and that is a choice down to the individual school, not a result of the existence of the NC or of SATs...
On the NC, I have a personal perspective that it is good to have the minimum every child should be exposed to in a codified form. I attended 5 or 6 primary schools, back before the NC. What was learned in each, at what age, and to what level, was wildly different. In some schools, I was accelerated by a year because I had covered in a previous school all that was planned for my age group. In other schools, I was with my own age group and had huge gaps in my knowledge compared with others in the class who had been in that school throughout. I did the Romans in EVERY school I attended, but learned no other history at all. Had the NC been in place then, the standardisation of age expectations would have made life a LOT easier - and it is that wild variation between schools that a combination of Ofsted and the NC have reduced..