Lot of ski "urban legends" going on here, IMO.
Believe me, when Rossi owned Dynastar and skiers like Alexis Pinturault were under contract, Rossi and Dynastar were collaborating on "a lot", and Pintu was their best rising male star. Most would suggest that the WC skis are made in the same race room, by the same people.
I could not tell you a thing about the retail skis, but that would surprise me, a great deal.
I've had plenty of conversations with the US race directors of both. That position is now combined into one, BTW. Plenty of collaboration, though they have cut back on North American race ski distribution.
Boots....Race boots made in the same molds. The compound used is different. You're a high level US racer, and they are coming from the exact same source. Depending on the situation, an athlete on Rossi might prefer the blue boot. Resi Steigler is one example.
Rossi is private held, re-acquired by the Boix-Vives family, and their PE partner. Laurent Boix-Vivres owned Rossi for many years; I'm guessing 30? At least.
Like many of these families of skis, the distribution piece is very confusing. Such as Blizzard and Nordica.