I agree with a lot of what you say about Khan in the video question and non-answer exchange. He should answer more clearly especially with reference (now) to the recommendations in the Casey audit.
It's quite possible there are other statements and recordings on record that are more positive about addressing grooming gangs but I suspect they'd get less amplification.
I'm pretty sure though that Khan loathes Hall for understanable reasons. He has credible threats to his life and to his family from fringe nutters and Hall has often strayed close to endorsing their views on "Londonistan". (E.g. liking tweets with this content). But the girls and women need him to step up.
A more useful question line in future would be for assembly members to quiz the mayor (and commissioner and probably representatives of borough children' services) specifically about their data collection and any policy and practice changes made in the light of reports into CSE in Rotherham, Oldham et al.
To be clear, I am not excusing Khan's response to Hall's question. But if one doesnt know the history between these two it would come across as looking far worse on Khan's part. I live in London so maybe come across more publicity about Susan Hall who isnt really a nationally known figure.
So I don't think he needs investigating. I don't know what it would even mean and don't know who it would help either.