Sorry if I'm not understanding correctly; but are you asking how to tell how stiff areas-that-you-designate-a-material are? / going to be?
IME, it is good to understand that the default YM (youngsModulus) 12 ^ YME (youngsModulusExp) 3 is, as Ziva has provided here in their documentation (https://zivadynamics.com/resources/ziva-materials), "representative of typical muscle tissue".
As you play more with the YMYME settings (along with fixed/sliding attachments) and let it simulate, you will get a feel for how stiff any given values are, and how stiff or less-stiff something needs to be for the effect you're going for. It becomes more and more important for speed (and your sanity hahaha), to isolate muscle groups as much as possible for finetuning, and then applying your findings to the whole later.
But from what I'm aware, unfortunately, I don't believe there is a way to see all maps up all at once (and as always, anyone with more experience than I--please correct me anywhere I am wrong). Since it is using Maya's Paint Attributes Tool, I believe it is a limitation of Maya.
If you're trying to stay on top of things like overlap, etc... for the meantime, screenshotting the weighting may be helpful, and is what I do.