You don’t have any proof about the true nature of Defkalion, but you DO have truth about Rossi’s other “customers” and “partners.” If the latter are shell companies related to Rossi, why wouldn’t the former be?
Because no one has established a definite link. Until they do, what I read from them is they were able to overcome some of the problems Rossi couldn’t and have made the tech more viable. That is within the realm of possibility, and a simpler explanation than a scam.
Not that I’m ruling out a scam on Defkalion’s part. Just not ruling it in yet either, and also not ruling in that they are in on it with Rossi.