You're missing the concept completely.
You literally want this game to suit you and you only.
What part of your statements give a general benefit to anyone other than yourself, or your friends that also have no accumulated enough hours to obtain Darkrai?
If you "rush" and complete your dex as "quick as possible" like you said you want to do, what do you have to do post-game?
If you've completed everything in the "400 hours" like you stated, what's left for you? Nothing.
So you leave.
So will everyone else if it's that easy.
Do you understand the flaw in your statement? Of how me saying your laziness is reason enough to not tailor the game to you, is reason enough to not lower the needed hours for Darkrai.
This will be my last response to you. My old father used to say: "You can't help someone that doesn't want to help themselves." That applies accordingly.
Good luck, for the last time!