They say that people should use the Pokemon they cherish most and it's available in-game, it must be used. But what's the point of it being used if there are restrictions for it from being used in official battle facilities and tournaments? The endgame legendaries have the worst treatment of this scenario because they're always overpowered, and they require you to use another endgame legendary, or a few selected OU Pokemon, to defeat it. It's something Game Freak will need to fix for people who love to use legendaries on their team so they won't be restricted to in-game use only. So far, I only have two solutions on nerfing them:
1. Reducing their base stats to 600 since that's supposedly the total number of stats a Pokemon is allowed to be used in a battle facility (Pokemon w/ base 670 are the exception because they have a nerf ability). However, event Pokemon are discluded because it must be Pokemon you could actually catch in-game rather from an event.
2. Limiting their movepool would also help nerf their OP status so regular Pokemon who also have shallow movepool could stand a chance. They've done it with the Tao trio, but apparently it wasn't enough to make them non-uber material because of their base stats (except Kyurem).
I really wanted to use a non-uber endgame legendary on my team, but my rules prevent me from using them.