I read somewhere that they don't have a lot of control over it. They buy whatever plastic pellets they can find and hope for the best. I would assume if they had the ability to make all their DX discs feel like these Thunderbirds, they would.
The same seems to be true with McPro plastic. The 2015 Aviars were much stiffer than the 2016's.
I'm sure you are right. Kinda goes along with the topic here.