So he wasn't a bad actor overall, good to know.
Sometimes bad actors turn in decent performances, providing the people in charge have that actor play to their specific strengths and take pains avoid their weaknesses. Dean Cain playing Clark Kent is a decent match. Not a GREAT one. But decent. But then again, you also admit the show turned to
shit. This not coincidentally lines up with the people in charge asking Dean Cain to go outside his wheelhouse. (There are other reasons the show went to shit, too, but I'm focusing more on Cain's role in it)
So why would people actually want Dean Cain, who played by most accounts (even those sympathetic to the show) a not great (if not flat out BAD) Superman, to BE Superman over 20 years later? If there's an actual reason beyond the surface "It kinda sounds cool," I haven't heard it yet. And I don't think that reason honestly exists beyond "it kinda sounds cool"
It doesn't take the reality of the show's casting calls into account, definitely.