Rex Campaign is a weaker Restructure on practically all matchups, since it gives a similar credit gain and must be protected to prevent it from being trashed. But a weaker Restructure is a small price to pay to get rid of Valencia's Blackmails, which can single-handely destroy any deck focused on big remotes and that makes it worthy of inclusion in Glacier decks in the post Order and Control metagame.
Even considering the fact that Rex Campaign can attract a Blackmail itself, three copies of it plus GNRLD Refineries and the natural protection of Ash 2X are probably more than enough to get rid of the threat. And when it comes down to it, having to protect it is not much different than not being able to play PAD Campaign against Security Testing decks so it's not a huge issue.
It's a nerf, but a tolerable one.