actually legendaries aren't THAT darn weak my lv100 azelf may only have 337 sp atk and 303 speed but with 1-2 nasty plots it can exceed alakazams 380+ sp atk. add that to an expert belt and it does a LOT of damage. i normally don't really use legendaries although now i will point out why some aren't ubers:
I am talking about Non-Uber Legendaries, of course. I always see people banning these, even though they have around the same bases as the OU pokemon. Let's take a look at those.
Ubers are pokemon who's base stat totals exceed 600, with a few exeptions.
BST= Base Stats.
Zapdos BST: 580
Articuno BST: 580
Moltres BST: 580
Entei BST: 580
Raikou BST: 580
Suicune BST: 580
Regirock BST: 580
Regice BST: 580
Registeel BST: 580
Mesprit BST: 580
Azelf BST: 580
Uxie BST: 580
So far, NONE of these guys have exceeded or even got to 600, so they are perfectly safe to use in the OU Tier.
Now for some more:
Cresselia BST: 600
Heatran BST: 600
These may look pretty high, but none are over 600. Besides, look who else has 600 BST.
Garchomp: 600
Dragonite: 600
Tyranitar: 600
Metagross: 600
Salamence: 600
That's right, some of the most overused pokemon out there today have the same BST totals of the previous 3 legendaries and have higher ones than the trios. So, if you ban legendaries you may as well ban Chomp/Nite/T-Tar/Gross/Mence, and if you don't, you're a hypocrite.
Furthermore, if legendaries aren't fair, then why are they allowed in the Battle Tower? The Battle Tower will let the Non-Uber legendaries in because they don't have the stats to be banned.
If you think you don't need to train legendaries for them to be good, then read:
Azelf Modest and untrained reaches 314 Sp. Attack and 266 Speed.
Alakazam Modest EV trained reaches 405 Sp. Attack and 339 Speed.
Now Azelf Modest and EV trained reaches 383 Sp. Attack and 329 Speed.
That means it still doesn't top Alakazam.
(Yes, Azelf may have a superior Attack, as well as some other stats upgraded, but D/P's Metagame is all about speed, hence people always choosing Jolly/Timid over Adamant/Modest. When there are things such as Weavile, Scarfcross, Aerodactyl, Alakazam[Shadow Ball], Agiligross, DDMence, and others running amok, the playing field is evened out).
So, WHY would you ban this if it can't even top a normal pokemon? Legendaries DO take skill to train, you can't just breed them for better IVs, and you need to EV train them just like any other pokemon. Level doesn't matter because everyone does Level 100 battles anyways.
~~~Exceptions~~~
Non-Uber: Regigigas
Sure, Regigigas has 670 Base, but his ability cuts his Speed and Attack for the 5 turns EVERY TIME HE IS SENT OUT, leaving him at 540 BST. Since no one else would have him out for more than 5 turns anyways, he is placed in the BL tier, far from the Ubers.
Uber: Darkrai, Wobbuffet, Lati@s, Mew
Darkrai has 600 BST, but his speed and moves/ability combination keeps him banned. Dark Void is a better version of Hypnosis, especially in double battles, and he has Nightmare/Dream Eater and an ability to stack on this.
Wobbuffet: His massive HP, moveset, and ability keeps him banned. He can kill nearly any pokemon, and take down a second one with him with Destiny Bond. Shadow Tag also doesn't allow them to switch out, keeping them trapped.
Lati@s: They have superior typing and an incredible movepool, placing them in the Uber tier.
Mew: When something like Smeargle has the potential to ruin teams just because of the biggest movepool ever, Mew will be an incredibly upgraded version of that. Put in Ubers because of a good stat build and a superior and an unpredictable movepool that tops nearly everything else.
~~~~~~~~~~~~~~
taken from B1001's marriland thread.