I hate Legendaries. Why? Because there is nothing legendary about them. Aside from the over abundance, the sole fact that you can have more than one through trading ruins the whole idea of "only one exists".

So I have a proposal for Gamefreak.
- First off, make less legendaries. Trio, Trio Leader, Pixie is all that are needed.
-Second: Make it so that only one of any legendary can exist in your game.

If you already have a Lugia, you cannot obtain another by any means. If you've traded for a Lugia and one exists in your game, it flies away. If a legendary is released, put it back into the wild. If a legendary is knocked out, have it come back after a while.

Treat your legendaries as just that: Legendary. One exists. If you have two Arceus in your party there should be a fucking paradoxical explosion.