MIMO streams and MU-MIMO are not the same. MIMO streams refers to the number of transmit/receive chains, which significantly affects performance. MU-MIMO uses beamforming to simutaneously transmit data to multiple STAs.The mimo streams is what the hobbyists will be looking at. WHich as Thiggins says its pretty meaningless and offers no benefit.
MU-MIMO has improved over time and I've seen evidence that it can improve total throughput in some test cases. But it is not worth specifically testing for it.
The new test process that I will be using when I resume testing will attempt to better assess product performance with muliple real STAs.