The thing that makes lower decks tolerable is the idea that it is basically non-canon. It makes the joke that Starfleet has minor expendable ships with crews that are routinely unprofessional, violent and given the lamest assignments (because the federation high command knows they suck) somewhat tolerable.

It's shame they're taking way too long to make Mariner actually tolerable as a character especially since its only in the later half of season 3 that she actually starts to face repercussions for her constant need to show off. Because if she wasn't in the show or was less obnoxious, a lot of the show's issues would simply evaporate.