This is cool... But I feel like having different color/brightness for each symbol kinda defeats the purpose of it being ASCII when the symbols only correspond to different intensities anyway.

Author here, I understand where you are coming from. However I did choose to keep it this way as it generally looks better. I toyed with other methods and I may introduce them in as a setting.

Yes, but it is "ascii art" and hence artistic freedom.

Yeah, with all these colors, any single character should be enough.