I know from personal experience that making a game is a very laborious task. Depending on the work done, 4+ years is really nothing when building a game by yourself. And I'm pretty sure that he has released more than one update for Patreons since posting this demo.
With that said, I'll admit that from the progress I've seen so far, the current releases are pretty underwhelming given the time he has used and the funds available to him.
I'll be saving my judgment for when (if) the final build is released. He could be making progress and assets that we haven't seen yet, and would account for the time taken.