How is it strange that Mack would chose themselves when selecting a ride for their park which exists, in part, to showcase their rides?
Texas Giant broke some records upon opening, iirc, but would you call it a chain-defining coaster for Six Flags? Also, how many high-profile accidents did it have?
Like I said, the notion of Zamperla getting some kind of major project from Cedar Fair isn't that strange. But there's a difference between a major addition at a single park, and refurbishing one of the most famous coasters in the world, at one of the most famous parks in the world, and turning it into a completely different ride. The TTD situation is an apple, and you've listed a bunch of oranges.
It's possible Zamperla's proposal, whatever if was, if a proposal was even made, was enough to convince Cedar Fair. I would still call it too risky of a move, for a coaster/situation that cannot afford risks.