Millie is pretty much a nothing burger and the shows refuses to expand on her
Because she is a normal Wrathian who happens to be a skilled assassin. She had a normal Wrathian upbringing, no traumas, no PTSD, etc. We do get some development stemming from this in season 2, where she considers herself just an imp and nobody important.
She goes to visit her family? Let's focus on Moxxie
It's because there's nothing of note about her traditional Wrathian family. They're just rednecks. The episode was about Striker, and Moxxie's insecurities.
She goes to visit Moxxie's family? Let's focus on Moxxie again
Of course the episode focusing on Moxxie's father is going to focus on Moxxie.
She is getting frustrated about how Blitzo is handling things after the break up with Stolas? Let's give a little attention to her then focus on Blitzo angst
Blitzo angst was only half of the episode. The rest of the episode showed how Millie deals with life stuff and her insecurities. I want to highlight her line "All this over a breakup?". That's how Millie handles things; she just tries to get over things like they're just another obstacle and keep going with her life. That's how she was raised:
You know, my mama always said, the best way to deal with being sad...is the sweat and blood of hard work. Washes the tears right off.
I want to see how she deals with breaking up with Moxxie.
she is supposed to be Blitzo's best friend
I mean, she probably doesn't have a lot of friends.
Moxxie and Blitzo are apparently closer
I don't think they're closer; they just have been together longer. Millie is a more recent addition to I.M.P.
I agree that they should have shown more interaction between Blitzo and Millie.
Maybe if she was a hellhound she would get more love
I don't know. Despite her popularity, Loona got less attention than Millie these past 2 seasons.