Welcome to Smogon! Take a moment to read the Introduction to Smogon for a run-down on everything Smogon, and make sure you take some time to read the global rules.
I feel like the drop of started in gen 2, but wasn't really noticeable because it and gen 3 did still have brilliant psychics, just for reasons other than being psychic.
Not including Miraidon because it's not really the same, Iron Valiant is the only well designed future paradox and the others should have been more like it rather than "What if X, but made of metal?"
I was actually thinking about Fire/Rock/Steel and Grass/Poison/Ground which are a Rock and a Ground self resist away from having the exact same interactions with each other as Fire/Water/Grass