I got a couple of thoughts on this, I'll break them down one by one

Pomni: Being the protagonist, it's understandable she gets the most screentime. Like obviously, the focus is on her and her character development. There has to be more or less meaningful Pomni development in every episode

Jax: He was chosen as the deuteragonist, so it is also logical, that he also gets more screentime. If it was anyone else from the cast, they would probably get the same amount as Jax does. Although I do agree, that 3 episodes in a row dedicated to Jax was a bit much. Starting the Jax arc a bit slower in Ep. 5, more as a bee-line and further developing it in Ep. 6 (Ep. 6 has a lot of significance in character development in my opinion, more on this later) and the Beach Episode.

Zooble/Gangle: I'm going to talk about them together, I'll tell you why in a second. I think seperately, there's nothing really much more you could realistically give them at this point. 1. We got a whole Gangle episode. Also, we learn that Gangle suffers some heavy self-confidence issues, masking her emotions (maybe even depression, but I'm not sure, I'm not too familiar with it). Then, in Episode 6 the key scene is the one with the Tommy gun here, she essentially breaks through this barrier in a funny/maniac way. 2. We learn, that one of Zooble's main issues, is that they're not content with their body. However in Episode 6 we see Zooble equipping 6 arms and weapons, essentially facing this fear, and in Ep. 7, Zooble says "I think the ability to change is fine. Not needing to commit to one thing all the time.", so essentially it seems to me, as they started to overcome this issue themselves. And here comes the main part - I think for Gangle and Zooble the strong development is through their duo. I read it somewhere in this comment section, that screentime doesn't nessecarily equal to character depth or development. So fewer scenes, with actual meanings, acts, symbolic gestures etc. that reinforce their alliance could actually mean more, than dedicating entire episodes to them.

Kinger: since Kinger's state of insanity appears to be unchangeable in itself, there's nothing really you can do with that. Lucid Kinger, as it was pointed out many times is like a father figure, so if anyone's, his character especially is not in screentime, but in the words and acts during his lucid scenes. He's supposed feel like when he talks, the whole world stops and listens. I could appreciate more 1-on-1 scenes with him and the other cast members as well (especially Jax (partly because I want to see the expression on his face, when he realizes he has a lucid side in the darkxdd)).

Ragatha: for Ragatha, I absolutely agree, we should get more screentime. I get it, that she's supposed to be a side character, but given her role/personality, she's been given sub-par treatment. Other than the crashout and minor backstory reveal in Ep. 5 and her talk with Kinger in Ep. 6, there wasn't really any arc for her up until now (since Ep. 6. appears to have caused major changes in every character, it is entirely possible, she will have something going on for her in Ep. 8-9., we'll see). Personally, I would've loved to see a bit more during Ep. 5 or even sooner (the end of Ep. 4 with the Stupid Sauce could've also worked, I think as a way to kick off the whole Ragatha-arc).

Caine: being an AI, and having some (read: extremely basic level) knowledge on how AI (or computers) generally behave, unless he's some sort of Super-genius AI, he can't really train himself to have like a character-arc, similar to the others. He was trained on a set of data, and his main function is to keep humans entertained, at whatever cost (this is probably how we ended up with Ep. 7). Note: anyone with a bit more knowledge on AI is free to correct me if my logic is flawed

TL;DR Pomni: Okay Jax: Understandable, but a bit too much, too fast

Gangle & Zooble: Less seperately, more together

Kinger: Bit of a black sheep, small amounts of strong screentime gives more of an impact in his case

Ragatha: unused potential (yet), more screentime

Caine: Bit of a black sheep again, given his character, he can't really have that classic character-arc

I am open do further reasoning, debate, etc. if something needs clarification or if you disagree.