There is a distinction between non-data-ink and redundant data-ink that is being made here. Whereas non-data-ink is usually easier to identify, redundant data-ink is somewhat subjective to how we view the information and process it. But you can argue that something is redundant if removing it doesn't change the amount of information contained within the chart that is required to understand and interpret it. However, you could also argue that different people interpret things differently, and therefore having different ways to do that will have some use.

Rather than trying to create unnecessarily debate, the intent is to try and help people understand the metric beyond a simple value but how the concept can be applied.

More importantly, it is not about simply chasing a perfect value that doesn't exist, but to optimize it within a specific context for your audience.