Personally, I didn't think the SATS was validation of what my child had achieved in primary. I felt there was a lot of wasted time in the last year what with the constant focus on the rather narrow SATS programme. and the Yr 2 SATS are even worse. I don't think this is at all the same as older students doing exams: they can thrive on focusing and revising for an exam in a way that small children should not have to do.
My dd is now doing GCSEs and I am very happy about that: I did not like the stress of SATS. And what I liked least about it was that in our primary at least it involved heads and teachers more or less lying to the children and parents: telling them that their SATS results were crucial for their future when the truth is that they are crucial for the headteacher's future, not for the child's.
This was the kind of reasoning that meant that my sick dd was pressurised into dictating her SATS to a TA at her bedside, being too ill to sit upright: because her friend who was also ill went hysterical at the thought that she might miss this vital exam- so the school sent TAs round to the houses of all the sick children. Or at least all the sick children in top set: I am not convinced they made the same effort with the low achievers.
Statistically of course, children who do well in SATS will usually tend to do well in later exams/at uni too, because they are that type of child. But that is correlation, not causation. Dd did not do herself justice in her SATS, but I expect her to do well in life.
And with all the levels and reports that you get anyway in Yr 6, I really didn't need the SATS to know how she was doing.