The XO was simultaneously great and terrible when he stabbed Mariner in the foot to prevent her from throwing herself into an apparently-unwinnable gladiatorial contest to save the team, saying it was *his* job as the senior officer to make the sacrifice play even if he had even less chance of pulling it off than she did. Especially since she just did a dramatic speech about it.
Honestly, I tended to side with him in that exchange almost fully, consider it from his perspective.
She's an Ensign, yes she's decorated, yes she's highly competent, but she's not the one who selected everyone for the team and knows everyone's capabilities, she's not the one in charge. Further, she doesn't necessarily know exactly his OWN capabilities, she's just
assuming she's more suited for the situation than he is. On top of that, she'd been insubordinate the ENTIRE mission and acting as if she should be in charge OVER an officer who seriously outranks her; remember, there's four rank grades separating them (Lt. JG; Lt; Lt. Cmdr; Cmdr), this is not a closely ranked senior subordinate lecturing him on how to run an away team, this is the junior most member of the officer corps trying to tell her how to do his job, one with a long history of disciplinary problems and other issues.
So yeah, she kinda deserved to be put in her place there, and in a subversion done right, rather than Mariner being shown to be right and having to save the day... he managed to pull it off himself while holding to Starfleet diplomatic ideals in a very Kirk-esq. manner.
To be honest, this was the episode that sold me on Lower Decks since it did this subversion. The first two episodes seemed like they were setting up Mariner as, well, an Ensign Mary Sue (and I mean that in the truest sense of the word, given the origin of the term
), but rather than doing that they actually actively, well, Lower Decks IS a deconstruction. It's a deconstruction not of traditional Star Trek (when it comes to traditional Star Trek the show clearly respects and loves it even while poking fun at it), rather it's a deconstruction of the recent trend of otherwise flat but faultless female Mary Sue esq. characters like Rey and Michael Burnam. As the first season progressed Mariner not only became less and less of a Mary Sue, she genuinely grew as a character and became more rounded and, to be frank, one of the major things that they showed through the series was that she was genuinely flawed.