Quality pixel art requires fine control of each pixel working together as a team to render exactly the intended shape and material within the restraints. Since we're dealing with computer-generated images it is easy to assume the computer can do all the generating, but what's not being considered is that there is a quality to pixel art that reflects the mood and care of the artist. The mind of an artist while pushing pixels determines the flavor of the finished product. There is a relationship between the pixels and the artist that you are underestimating Howard Day. Which clusters of pixels to keep and which to alter? Does it look better like this or like that? An artist makes these informed decisions with experience. This is why it is an art. The artist puts himself into the pixels and the computer screen gives instant output but when is a piece of pixel work complete? The artist decides. The artist guides the pixels towards a vision with time and care.
If an artist writes instructions for where pixels should go and the computer carries them out, it is not the computer's fault if the output pixels lack quality placement. The end result is still the expression of the relationship between the pixels and the artist (the programmer). It is possible to write a program to generate pixel art, but the resulting art should not get a pass on standards only because the computer is doing all the heavy lifting. With an adequate understanding of the subtleties of what makes certain pixel combinations beautiful and others unthoughtful, plus the skill to execute such understanding with code, quality pixel art could be produced by an artist's programming commands. This would be heroic and quite admirable to witness. You still have much to learn about this subtle pixel technique though.
You can't just go around dithering everything and call it pixel art because it's "close enough". Trust me on this.
I've got a pretty solid grasp on dithering and I am still not churning out quality pixel combinations like the best. There is no shortcut to putting in hours zooming in and out fine-tuning pixel placement one pixel at a time. I've tried. And while we can tell you things that could be changed with your filter here and there to help your program "create better pixelart-like output" we are only holding you back from discovering your own relationship with pixels as you learn to understand the reasons our suggestions make the output look "better". By all means use this project to expand on your craft, but don't use it as a reason to avoid learning the 1x1 pencil tool, instead realize the more time you spend with the 1x1 pencil tool the better this project will become. I am not trying to kill your motivation for your project! I like it and I want to see it become the best it can become by trying to get you to ask yourself pixel art questions. Good luck.
