So it seems like ultimately, what they've done is to move what used to be "Red" into "Red Pro" and make "Red" a more budget oriented line (without clearly communicating this in advance).

The only reason to do this is to trick customers into buying the wrong product by accident! There is literally no good faith reading of this change. If they wanted to provide better value for the people who don't mind the SMR performance characteristics, that's great, but that would involve clearly marketing the line as such, not simply redefining what "WD Red" means.