I agree. It does feel to me that, like the first class prosecutor he is, Starmer is systematically destroying the defence and credibility of the PM. It helps that there are continually so many things to choose from, but he has his measure fully now. He knows in advance how Boris is likely to respond and he knows how to phrase the question accordingly to trap him into exposing his weaknesses.
For instance, Johnson must have known he was going to be asked about the exam fiasco and had worked out a general deflection plus standard counter attack response in advance, but Starmer wrong footed him by going very, very specific. He knows Johnson doesn't do detail. This meant a general brush off waffle response was starkly inappropriate. Meanwhile the question still got the exams fiasco to the fore, but now linked Johnson much more personally to the **** up, than just being the leader who had appointed a minister that failed.