Remember, Alakazam is just as powerful and not much slower. Dark Void is, in my opinion, what broke it, so I think without that he would be OU very easily. He still crumples under Breloom's Mach Punch.
Darkrai's defenses aren't bad, but it has zero useful resistances. It would be a somewhat-faster-gengar that:
1) can't switch into anything (missing those immunities)
2) doesn't have disable
3) doesn't have pain split
Basically flawless 2 move coverage, fair bulk, and Nasty Plot are nice but... well, if you thought Slaking's lack of resistance would be a problem, just check this thing's. Darkrai would struggle to maintain its OU spot. It'd be in OU for sure (thanks to the fan boys), but would not be a top threat..
You're right about this, but to be fair it's actually not that big of a deal. Take a look at Zam, he doesn't have any of these qualities either, yet his usage is still very high.
Looking back to the TR discussion.
What if instead of serene grace, jirachi got an ability that summoned trick room for as long as jirachi was in play?
Actually if jirachi holds iron ball it would be able to go down to 90 speed which is slower than anything without a -speed nature except for ferrothorn. So comparing it to the scarf set in exchange for 30% extra flinch chance it outruns far more threats, can invest in bulk, and has the freedom to switch moves. Not to mention most trick users would absolutely hate getting an iron ball and jirachi could even run trick itself to cripple something with iron ball or swap around anything it gets tricked. Even without iron ball it's only a bit faster than neutral base 70 speed so it could also run some sort of life orb or choice set and screw with offensive teams (which is likely much better than something like iron ball actually since a bunch of things slower than base 70 have the bulk to deal with jirachi anyway).
Yes, but is that really enough of a reason to run it over Serene Grace? Just to Trick an Iron Ball? Besides, Prankster Sableye does a much better job at pulling that off anyway.
The only thing you're really sacrificing compared to the scarf set is the 30% extra flinch chance.
30% extra flinch chance is pretty big though; nobody likes being Haxrachi'd to death. Jirachi's also fairly weak without a boost, so anything with decent bulk that doesn't mind being Tricked an Iron Ball can set up on it, and even hyperoffensive teams have Scizor/Breloom/etc.
That's nothing compared to Tinted Lens. The Banded Set on a resisted hit does more than Kyurem-B's Outrage on something like, say Forretress. Tinted Lens would be a great ability for Flygon for a matter of fact. It's already outclassed by Garchomp as a wall-breaker, and adding U-turn to the mix makes it actually have CONSIDERATION over Garchomp. Noone use Flygon anyways, even with Leveitatae. It has a niche on VoltTurn teams with Earthquake problems, but nothing else. I would say Tinited Lens would plummet Flygon's utility as a wallbreaker. Think about it this way. DragMag is cool, but now what? Flygon turns the point of DragMag to a liability.I think that levitate is still the better skill. Ground/Dragon is solid coverage to begin with, and you've got two other moveslots for moves like fire punch, stone edge, and superpower. It might be worth dropping the ground/spikes immunity for fire blast and sub/toxic, but I don't see it rising to OU due to this ability.