This is a great example of working out constraints within a genre!
With Passpartout, figuring out how much a painting should cost was complicated with so many pixels to considerate. So time was the measurement to reward the player.
Now, your game reminds me of speed build battles in Minecraft servers, mixed with the previous game, where you use pixels to compare a win from a lose, which allows you to concretely reward the player instead of relying only on how much time you spent drawing.
Simple and effective!