I know it’s not free and I would be prepared to pay the $100. I would spend a lot of extra time making a full game with lots of extra gameplay. The reason I would choose steam is because it’s a more popular platform than itch (Most people don’t know about itch), so less people would play my game if I just chose itch.
Viewing post in Should I turn my game into a steam release?
I'd use YouTube and other methods to promote. I've read about itch and I don't think it's the best platform for full visibility, although if I finish it properly it will be uploaded to itch.
If you really don't think steam is a good fit, that's okay, I'm not going to critique your opinion of steam. What I might ask is—on any platform, is the core idea good enough for a full game release with several more months of work?