Siren seeing Diaz having no qualms about burning people alive has her shook and now she is afraid to go against him even when it comes to Quentin. All good, fine, but what is stopping her from using her Siren Scream and just taking him down? If the writers wanted to take this path with her (which I am totally fine with) then there has to be something more that is stopping her from retaliating. Even a simple line while talking to Quentin "I've thought about screaming his brains out but he has sonic dampeners stopping me" BOOM, I can work with that. Makes sense. But they never give it to us.
Siren being scared of Diaz makes little sense. His burning a guy alive is not much different than her screaming in Vigilante's ear from inches away. She likely did much worse back on her earth.
I did think it may be Diaz' new partner that she'd now need to be weary of, but for all involved purposes, she could probably easily despatch of them too, however...
To make sense of it, I do think she genuinely cares for Quinten, and she probably knows (or suspects) that he she betrays Diaz, he has something, or someone in place to take Quinten out, so she's playing ball for Quinten's sake. That's the only sense I can make of it.
That said though, much alike a Cry Dampener, it would have been nice if there had been a scene between either Diaz & Laurel, or Diaz and someone else which stated, or implied this to be the case - just so we know exactly what her motives are, but on the flip, that would take away the suspense and speculation.
The Oliver/Diaz fight was good, I enjoyed it so I am happy that they had Diaz end the fight by being dirty and using all of this as a driving force for Anatoly to shift his allegiances. Though I a guessing the dude doesn't know that Diaz killed Cayden while he was helpless to do anything? Or does he get a pass since he was willing to sacrifice everyone?
I've always liked the character of Anatoli, he's often walking that fine line, though he does have a sense of pride and honour within him which keeps him on the straight (as far as a criminal goes).
And did no one else watch the next week promo in slow mo? How are we going to explain the next guy in the Arrow suit repelling into court? From another earth? Dibney before Devoe got him? A guest appearance by J'onn? Trying not to spoil here.
Spoiler Tags may be prudent.

Needless to say, aside from crossover events, I wish they'd leave the doppelganger elements of the Arrowverse to the Flash show. If they want to do multiple Earths, that's great, but not on Arrow please. Whatever you may have seen likely wont be John or Ralph either. As far as I'm aware, these shows are currently happening in real-time, so at this point in Arrow, Ralph I dead, and I don't believe anyone from this Earth knows that John can transform into other people (though they do know he can disguise himself in a human form).