If HW was serious about the game he would have been able to put it up as Early Access years ago with a polished version of the first level, then work from there until everything he wants has been added to get to the 1.0 version.Considering he did cobble together the demos at the last minute once the steam approval went through: I do believe him now about being denied before. Not because of any error on Steam's part, but due to his own incompetence and user error when it comes to submitting the game. Then again looking at him blatantly lying about Patreon pledges makes me feel like a fool for trying to give any benefit of a doubt.
The early access titles I've bought worked that way, a more recent example is Gloomwood. I bought that the very day it went on Early Access and it only had the initial tutorial area, the mine area after the tutorial area before stopping at the area just outside of the mine exit. A little over year later and a lot of new areas, enemies and features has been added, while existing area and enemies got even more polish. It'll be getting another huge area soon with new enemies as well which would make the game around 50% complete.
I'm guessing HW doesn't want to do the Early Access model because that would mean that once people got the $20 threshold needed to get a Steam key, a lot of backers will likely stop there and just wait for the updates to come out on Steam.