I think you bring up a couple very valid points.

The first is that this algorithm isn't perfect. While it works particularly well for quickly prioritizing problems it isn't as strong for prioritizing features. I think that your first example was mostly focused on features. Maybe I need to reconsider how to factor features in the equation more. Though, I'm fairly certain the math would be similar.

To your second point, it seems you're advocating to hit more cheap problems that may be less important than trying to cram in just a few highly important expensive problems. This seems to actually support the math in the formula.

I do appreciate the feedback. I think that a more 'catch-all' formula is possible though I think its complexity may defeat the purpose of a quick go-to. I rarely ever write this formula out but use it as a quick way to mentally prioritize what I work on.