>>32334153I don't think it's a coincidence that Gen 4 was both the last good meta, and the last meta with Team Preview.
Team Preview drastically changed the nature of battling; whereas before you'd have to account for your opponent sandbagging checks/counters for your sweepers, you can now just make sure you kill them and go to town. It's part of the reason trapping got even more powerful than it was before.
We can sit here and talk about how [Pokemon ___] killed competitive Pokemon (looking at you, Landy-T), but really the problem is more structural.