The way I took it, Raven simply wrote of “repeated machine-gunning of survivors in the water.” This was in relation to DORSETSHIRE (box art).
Agar’s report can be read as confirming this: “a number or aircraft… first machine-gunning personnel as they were getting down the side, followed by several bursts of fire into the water.”
I suspect the DORSETSHIRE survivors in the water on the receiving end of those “triumphant joy” bullets from “a number of aircraft” would have sympathy with Raven’s idea that they were repeatedly strafed.
However you seem to have a deeper understanding of Raven’s words interpreting them more darkly as saying the strafing was “willful, deliberate and sustained”. I did not take his words that way but if that is the case then I am with you – there was no attempt to exterminate the survivors.
Turning to the oft-repeated quotation from the CORNWALL survivor about the flypast and non-machine gunning of survivors, I think that must be read in its original context. The words are those of Cdr Fair (Capt Manwaring was wounded) from his report on the loss of CORNWALL and refer specifically to the experience of the CORNWALL survivors in the minutes after CORNWALL sank:
Photos show that DORSETSHIRE sank before and some distance from CORNWALL. I believe it would be incorrect to use these words of Fair as evidence there was not just the brief bit of exuberant machine-gunning of DORSETSHIRE survivors that Agar reports whilst attacks continued to finish off Fair’s still-afloat CORNWALL.