Let me take this apart piece by piece.
She is one of the most annoying champions to lane against just because of her stupid 2 second stun.
Her stun isn't 2 seconds until max rank, and nobody maxes Equilibrium Strike first. Laning phase doesn't last long enough for her stun to reach 2 seconds (Level 13). The highest it gets is 1.25 seconds during laning phase (Level 8).
Riot makes cc scale up towards mid/late game because you need longer crowd control during team fights, but you don't want to lane against a 2 second crowd control effect because it'd be unfair to trade against. So Riot sets cc at about 1 second during laning phase (some champions even as low as .5 seconds).
She outdamages any champion full-ap/ad champion with just Tri Force and builds full tank.
She doesn't out damage any champion, or even most for that matter. Riven and Cho'gath are prime examples. Both of them easily win the lane against Irelia, and out damage/out scale her late game.
For squishy champions (ADCs and APCs), it seems like she "out damages" them because they're too busy trying to escape to fight, and because they're too squishy (unlike Irelia) to stand there. Her gapcloser and stun make it to where they need to escape melee range before they can think about fighting. That's what a mechanic called "kiting" is used for. She can easily be kited due to the considerably long cooldown on Bladesurge. That's why she's given a long slow/stun; so that she can at least stand a chance against kiting.
In other words, she doesn't out damage any ADC or APC, she's just tankier. If kited properly, an ADC or APC can beat her.
Snowballs way hard. If you get killed by an Irelia there is no coming back.
Not true at all. If you play properly and farm properly, you'll come back pretty quickly. If you get killed a second time, however, of course you'll get snowballed. By that point, you've already lost a considerable amount of cs and gave her 578g in kills. That's why you PROPERLY tower hug, and make sure to just last ht whatever minions you can at a safe distance. You'll come out of lane behind, but at least she won't be too fed.
Impossible to duel because of her stun. Her low cooldown and high duration stun makes her almost impossible to duel.
Umm... First off, most of the champions in the current meta have crowd control, some of which are better than Irelia's. To name a few, Riven, Zac, Cho'gath, Sion, and Gnar. Her stun also has the average cooldown of a stun, 8 seconds. And to make it worse, it doesn't scale down by leveling it. Throughout the entire game, it's 8 seconds without Cooldown Reduction. As well, again, the stun is only 1 second and 1.25 at level 8. It's not that long of a duration, especially with the current meta.
True damage and sustain, targetted dash, etc. Her ultimate has almost no cooldown.
Let's go back to the current meta ramble I was on about. Cho'gath has a true damage ult and immense sustain with his passive, and his ult cooldown is only 80 seconds. Zac has % max health sustain that is pretty high and annoying to deal with, especially in lane, and his ult is a large amount of crowd control which gives him a movement speed bonus and 36% of his max health regenerated (if you properly pick up the blobs), the cooldown being 130/115/100. Riven has a shield that scales off of her main stat and two ultimates that output an immense amount of damage, and her ult cooldown is 110/80/50 seconds. Gnar's passive regens a large portion of his health, and his ult gives him two extremely long duration crowd control effects, with a cooldown of 120/110/80 seconds. Irelia's ult doesn't put out a large amount of damage, but gives her back 25% of the damage output by the ult, with a cooldown of 70/60/50.
You may be thinking, "This just proves my point!" No. Her ult is weak compared to all of the meta champions. You heal about 300 health, big deal when you're getting wrecked by a Riven shield and ult; crowd controled by Zac who's healing a % of his maximum health and dealing damage at the same time; knocked up, then silenced, then eaten by a Cho'gath; stunned three times in a row and being out damaged by a Gnar. Her ult is extremely weak in comparison to toplaners of the current meta.
Her passive gives immense power in teamfights.
This is true.
She can straight dive to your carries and delete them.
No she can't. If your team is playing how they're supposed to play (2 tanks in front, bruiser in middle, APC and ADC in back), the tanks can at least get a slow off, giving the carries time to back up, which allows the bruiser to peel them off while one of the tanks comes up to completely peel off the carries, meanwhile the carries should be kiting properly.
So when will Riot nerf this champion?
Not anytime soon. She's perfectly balanced for the current meta. Get good.
and enjoy the free lane.
gg
as well while you're at it.