IIRC, when Betza was considering cannons, he concluded that a standard cannon (move along rook lines, capture by hopping along rook lines) was likely stronger than a bishop, but thought that replacing bishops with cannons in the FIDE opening might not reveal this advantage because it would make development too difficult. He commented that "even replacing bishops with rooks is not that easy", or something like that.
I'm curious, have you tried a test where one side replaces its bishops with additional rooks?
Also, is your testing software available for others to use? I try to assign values for importing the For the Crown pieces into something like buypoint chess, and it would be nice to check my guesses against a computer. I think I asked this once before and you suggested I wait for Sparticus, but it's been some time...