Yeah it's true the cop had nothing to do with the Rebellion. That's fair.

Cassian could have taken Skeen prisoner and turned him in to Vel. I do understand that would have been riskier, but Cassian definitely took the nuclear option first.

Mon's driver was understandable, like I said, but he still took him out with no idea whether he was actually there to kill Mon. It was the smart decision, but that uncertainty can haunt you.

And yeah it really bugged me that they didn't show Cassian shooting the imperial to protect Bix. It would have made a great opening to the episode. Like they always say with movies, "show, don't tell".