Sad to hear Below Zero is suffering development troubles.
Regarding map size, TBH Subnautica's map was too large with too many dead zones where it was never worth going. Starsector also suffers from pointless empty areas (star systems with no planets, for example), though some of that could be filled with new types of content.
I never got into playing Subnautica despite it being one if not the best exploration games of the decade.
One of the things that contributed to that was the developer's decision to cram it's own identity politics into it. For example, did you know that the only item in the game that is meant to hurt animals was and still is the standard knife?
There is nothing else but an itty bitty butter knife in a game with 30 meter long translucent sea snakes that want to eat you because the company, under their own admission, is for animal rights and found it wrong to give you anything else to defend yourself with.
Not for story, not for immersion (pun intended) but simply to have their game reflect their personal agenda. I will not take away any of the game's stellar features but developing games this way overcomplicates the already arduous task of creating something people will play and have a blast with.
What's worse, you take away one person leading a developer team team this way and the whole project crumbles like a sand castle. It's exactly what happened to Subnautica Below Zero when the lead story developer quit/got fired and was replaced. They're re-doing the whole story over.
Aaaanyway, back to Starsector, I personally think system variety is fine as it is now and for one basic reason: exploration is not about guarantees.
Would you still go fishing if you knew for certain that every time you threw your hook in the water, you'd catch a fish?
The same applies to solar systems. Having every map guaranteed to contain at least X takes away much of the thrill of exploration for me. You don't know what is out there, you don't even know if there IS something out there, therefore you keep searching.
Edit: Typos, they're coming out of the freaking text lines!