Perhaps the PDGA should add a tolerance to the maximum weight per mold, like +4 or so grams
I have worked in an industry where limits were necessary. I found that when a tolerance was added (i.e. 175 +4 grams) you ended up with a new limit, and that was 179 grams. So then the question becomes, why can't I use my 180 gram disc. So you might as well just set an upper limit and then decide how to (or not to) enforce it.