Ah, I understand your question now. If you want to be able to rank gear with a custom strategy, you have to run a "gearing strategy" type simulation. It can take a long time - an hour or two depending on your computer.
Here is a guide on how to set it up:
You don't nee to worry about step 4 anymore. For a healing gearing strategy on mythic+ you will want to make sure to set your mythic+ level to something challenging for your character. But not something so hard that everyone dies.
If you run a single simulation and set the output level to log, the report has a section labeled "other". If you expand that, you will see how many times your allies died. Aim for a mythic+ level where your allies die between 0 and 1 time, on average.