(you told me on reddit to go here, so here i am)
I've developed a small tool myself to measure the effectiveness of resto druid mastery so that players can decide how high to value their mastery when doing statweights.
What you've build atm is cute but not actually usable to make descisions on.
For every HoT we have a "stack" of mastery on a target, so mastery is more valuable when you on average have more HoTs on the targets that you're healing.
My tool tracks the stacks on targets and shows an average:
It's a bit raw and needs improvement atm because it just counts the stacks, doesn't take into account how much healing respective HoTs do nor how much direct healing you do on targets, but it's a decent indicator.
an improved version would attribute it based on healing done on targets.
you said your code ain't open source, so I can't contrib it to your project, but having it in checkmywow seems more useful for more people to have access to it then my seperate tool.