I'm not going to get too deep into psychoanalyzing Jeph as to how much he realizes what's working or not. He could honestly believe that or it could be denial. I feel like if I could understand WHY he loves her, or give a reason for that it would go a long way to writing her better.
I'll send a DM since it's occasionally NSFW. nothing too explicit, just a butt here or there.
If it bothers me enough I will end up making my first video essay ever about this topic. I wanted it to be about particularly interesting encounter design in old D&D modules but lord help me I've got a bee in my bonnet over this.
Being generous Liz is supposed to be representative of the victims of broken systems that leave people to the wayside and the folly of being a "gifted student" with expectations and pressures.
But you bring up another point of thing that separates Liz from other Gremlin characters. Marten, Claire, Bubbles, and basically everyone can just leave at any point. They are in no way attached to or imposed upon by Liz. They are willingly associating with her for some reason. Usually with this archetype they are either stuck with the Gremlin or the Gremlin imposes upon them at every opportunity and won't leave them alone. From the outset Liz wanted to be left alone, and her entire introduction was a ploy to have people not notice her existence. Martin and Claire are under no obligations to take care of her but do anyway for no discernible reason other than Liz is in the cast now.