Netossa and Spinnerella were the only members of the Princess Alliance before Adora joined the Rebellion, yet they didn't say or do anything until the battle at Bright Moon, and haven't done much since; even in the fourth season, their focus episode was largely focused on Glimmer's arc. We know little beyond them that they're in a relationship, that Spinnerella likes vegetarian snacks, and that Netossa is fairly competitive. As Bow himself puts it in Season 1 Episode 4 " "We're not really sure what they do." Averted in Season 5, when Netossa and Spinnerella receive much more screen time.
Huntara was a big Ensemble Dark Horse from the original series and has the powerhouse casting of Geena Davis. She makes a big impression for a couple of episodes, then disappears without explanation. She then only appears in a single episode in Season 4 (and a short cameo in the series finale), though at least this time she does get proper closure.
The series put a great deal of effort into making villains from the original series both competent, but also humanized. Original!Imp was both, proving a Not-So-Harmless Villain through his cunning and spywork, and being the only Horde member Hordak to cared about. But this version is effectively mute and treated like a pet to the point of an of ambiguous sentience. His stealth abilities did help shape major events in the Fright Zone in earlier seasons, but he only appears a handful of times in Season 4 and only makes a brief cameo in Season 5. "Huntara" implies that he is a clone of Hordak, but his genetic connection to the Galactic Horde and emotional connection to Hordak never becomes relevant.
Season 5 has been criticized by some fans for squandering multiple characters:
Double Trouble was a fan favorite who played a major role in the events of Season 4 due to their shapeshifting abilities and fondness for chaos. Aside from a minor side plot in "Perils of Peekablue", Double Trouble plays no role in the events of Season 5.
Lonnie, Kyle, and Rogelio, who were previously recurring supporting characters in Seasons 1-4, don't appear at all in Season 5 until a short scene in the finale, and don't interact with Adora or Catra.
Razz had firsthand knowledge of the First Ones' conquest of Etheria and the unique ability to interact with people in the past and present, but none of it ever comes into play in Season 5. She appears for five seconds at the end of "Heart, Part 2".
Many Hordak fans were disappointed that he only appeared a handful of times in Season 5, despite his rich potential for character development, knowledge that could have been useful to the Rebellion, and position in the Galactic Horde that could have been used to show viewers more of clone life.
Micah gets so little to do in S5 that it's hard to tell why they even brought him back in the first place. He gets one episode to do anything, it's early in the season, then he's chipped, and his reunion with Glimmer afterwards is given about four seconds - his relationship with Frosta, who he's not even related to, is given more screentime.
Mermista and Scorpia are chipped about mid-season and don't get to do much afterwards.
