It makes perfect sense that diamonds match up with predators for many reasons, and should stay that way.
Predators are the best of the best. To get there, you should have to be exceptional at the game. What better way than maintaining RP growth through 2800 points among them. You consistently play against them, prove you’re better than them, and you earn the right to have your rank displayed among them. Makes perfect sense.
Playing against other diamonds would only prove you’re better than other diamonds. Then, you would hit predator and be smoked by the people there. That brings up the question: Do you really belong there if you can’t hold your own? The answer is no. It is the highest rank in the game and you can’t be demoted out of it.
You aren’t entitled to anything. Anybody could hit diamond if they played the meta, adjusted their playstyle to fit ranked, and played the placement system. However, not everybody can hit predator. The ranked system isn’t “too hard”, when other people did it just fine. It’s too hard for YOU. Focus on improving, not on complaining.
Side note: There should absolutely be a system in place to be demoted out of diamond. The amount of people who got carried for a lucky win streak and are hard stuck at 7200, or plat 0, is insane and ruins the quality of games for people who are climbing and actually belong there.