Hackett had little to no knowledge of Shepard's location or if he was still alive, and even then, had Shepard's blessing to go ahead and destroy the Reaper.
I'd honestly call that selective blindness on your part to not see a difference between Hackett and Gerrel in that situation.
And I told Gerrel to press the attack. As I've argued before, retreat via relay (Shepard's alternate suggestion) was not feasible.
Believe me, I'm not happy about him cutting off comms and I say as such. I'm pretty sure Hackett knows we're alive and where we are, given that Shepard radios in and gives the order to either save the Council or target Sovereign minutes earlier after opening the ward arms. Hackett doesn't try to re-establish contact, he simply orders the attack. I don't hold that against him either. Neither had any idea how long it would be before their respective targets came back online.