If you only take that idea in one direction then I agree that it is pretty silly. However, the spirit of the visualization suggests finding a balance and optimizing the data-ink ratio rather than searching for a perfect value. If you follow the link you'll find the article I wrote talking about this: https://scienceux.org/articles/data-ink-ideal-vs-minimal

All the points that you make are very much valid, and it is good that you have pointed these things out because I wouldn't want people to follow these principles blindly without thinking about it for themselves.

I haven't considered the 'ratio of integral of norm of gradient of colour' too much (because it is easier to start simple and build on it), but I hope you might consider elaborating on it.