I'm not finding the tactic of making emotional moments out of parting with characters we hardly know to be terribly compelling.
Do we know why they wrote the character of Nhan off the show? It's possible the actor wanted/needed to leave, and they did the best they could to give her a decent good-bye.
Airiam's exit was likely due to the original actress' developed allergy to the prosthetics and make-up . . . although by the time they killed her off, another actress was playing the role. Did she develop problems with the prosthetics also? I do like how they brought back the original actress, Sara Mitich, in a new role, the new blonde lieutenant Nilsson who just seemed to appear out of nowhere! Will the replacement (and killed off) Airiam, Hannah Cheesman, get to come back in another role also?
I liked Nhan, I was glad when she decided to jump into the future with Discovery, and now bummed she's off the ship. It was a good character moment though, and did underscore how isolated the Discovery crew is feeling jumping centuries ahead of everything and everyone they knew. Both Nhan and Saru had emotional moments when they learned their respective worlds had joined the Federation after they left the timeline.
But yeah, I really like the B-cast of Discovery, but their character development has been weak for the entire show. At least it's not as bad as season 1! Although to be fair, the original series (TOS - Those Other Scientists) crew didn't get much more development either. It would be nice if the Disco crew got the kind of attention given during the TNG/DS9/Voyager era.
Also, was that the actual USS Voyager at Federation HQ, or a successor ship with the same name!?!?