What is the basis of this assessment?
I watched the trains at South Keys today, which I consider the weak point of the line, because the track is shared by both Line 2 and 4. What I saw did not build confidence. They were running trains on both lines, but they were unable to operate either line on the contracted 12 minute schedule. The airport spur was running every 14 minutes (while I was there), and the main line was worse. Trains were delayed by signals, and because the trains were not matching up at passing locations.
Given the single track design, trains must be in the correct positions reliably before this project can be opened. With 9 trains and 6 single track sections, this will be difficult to get correct. It is not ready, and I dare say, there will need to be a lot of improvement, before a final test period can be started.