You indeed only gonna see mostly the bad news on the forum, complainers are eager to complain but people doing good rarely tell about it. Probably it has something to do with fear for competition, maybe people don't like to reveal the location they found some gold?
I’m doing sci-fi most of the time and its going well.
When doing unique design competition is going to be less of an issue.
Just do the stuff that inspire you the most then you gonna feel most fulfilled. Its not going to be so hard to make it a success if you like what your doing. Focus on creating value and try improving that on constant basis. There is allot of room in sci-fi genre and demand for content in this category is growing. Some focus on weapons others just on armors, some may do corridors or sci-fi panels, etc., and they do well. However keep in mind there are already items in there so you need to clearly distinguish there (https://www.cgtrader.com/3d-models?keywords=sci-fi+weapon)
Alpenwolf seems to be doing very good in the sci-fi weapons category (https://www.cgtrader.com/alpenwolf)
Littlechild also seems to be doing relatively well in sci-fi genre with a small library (https://www.cgtrader.com/littlechild)
Mykola has a small library but it seems to be doing very well (https://www.cgtrader.com/mykola1985) clearly has a few top selling models there, looking at his reviews the robot is probably the top selling item.
You can visit more pages from successful designers (https://www.cgtrader.com/designers) and see what they are doing.
You can recognized successful designers on reputation points.
When designers sell something the amount they have earned will translate to reputation points so you can see some crude figure regarding revenue made. Note however, getting likes and activity in the forum also gives some reputation points. People providing free models also get some reps so view on actual revenue is somewhat blurred and you need to dive in to get better picture.
Anyways, I can recommend producing work for sci-fi genre.
