I don’t have a problem with the 10-12 mm size range myself. I agree it may be a waste of material which does in fact sting but for me the bigger picture is the importance of the competition. I will buy a piece that is appropriate for the competition and have always been glad to see that they most often let you use lab created material which will keep the cost of clean material down.
I do have an issue with the choice of materials to a degree. Last year I had to find a spinel which I had never cut before. I was able to locate a single piece of it on Ebay and it was heavilly cracked. I was barely able to extract one piece from that boule which would fit the sizing requirements but I guess that that is part of the challenge itself: how to cut around bad rough.
The issue of girdle thickness is something that would bother me if I were to use a competition stone in a setting but the .3mm thickness requirement is set to test a cutter’s abilities. These stones are not meant to be used for jewelry, they are meant to test you.