The point is that it's so outdated, it's pointless busy work.
Their methodology wasn't necessarily inherently flawed, but the existence of time means that the assertion that results are now the same is utter bollocks. It also doesn't measure progress, as that's not monitored in a comparable manner in independent.
They were consistent attainment results at the time those date points were recorded. However, seeing as the DfE completely buggered up the data collection for this year, there were two years with no comparable data and political decisions have affected the examinations/syllabuses/testing so assessments at end of phase are very, very different from those in 2017, it's pointless and will be misused forevermore.