The b-plot fell flat and took away way too much time from Morty x Planetina.
Agreed. As far as romance/consequences/absurdity/pathos plots go, it wasn't very deep. They've done it a lot better in the past, like the hive mind episode, or the time crystal episode, or the love potion episode.
Agreed that the b-plot was lacking and also took too much time from Morty's plot, which needed a lot more development. Starting the episode where Morty has already met Planetina and everyone accepts that she's a normal thing that exists on Earth for the past 40 years was a little jarring. Planetina's heel turn was as nearly underdeveloped and out of left field as in Game of Thrones. I can understand the logic of Planetina's actions, but it felt more plot driven than character driven. I'm not even sure if I'm supposed to understand that this is a natural consequence of killing her kids, and that although they were fuckers they were actually keeping Planetina from going off the rails.
Speaking of which, what the fuck happened to the rings? Wouldn't Morty be technically controlling Planetina since he has all the rings? I feel there's a missed opportunity for some Sauron "unite the rings under one ruler" or Mandarin type shit, but they did nothing with the rings.