I’ve been in this discussion before. Talking about FIS race skis in SL and GS. I have no info on current seasons skis (have a hard time believing it is changed though), but the previous seasons we have had quite a few Rossignol and a few pairs of Dynastars. Only been the top sheet that differed. Flex did indeed vary on ”identical” skis, but that wasn’t tied to brand. Seemed random to me.
Also heard about Lange Rossi plastic. Don’t know if that is myth or truth. We’ve only been in Lange. The mold, buckles, strap etc. seem identical.