She is overloaded. Just like yasuo still is. You can ask yourself what kind of ability does this champion lack? nothing! it has everything you could ever want on that champion. Riot is so good at making broken shit designs that have one-man-army kits. what is it irelia lacks that she has to play around/get from an ally? absolutely not a single thing. she has: hard aoe cc, basically a invulnerable spell, same damage as a carry, tanky, the new ult can be as effective as a stun wall, she can also make her damage turn into true damage. she even has a mechanic to make it irrelevant if you buy items to specifically make it harder for her to kill you, that has to be the definition of having a overloaded kit. I guess the only thing that could make her even worse would be if they did the same thing they did on yasuo and make it so that if she takes to much damage her passive gives her a spell shield instead of giving her more damage. So there are champions that are even worse. But irelia already has a ability to make her basically invulnerable so she already has that mechanic. Thing is, nerfing the champions numbers is not gonna fix it. sure it will eventually get them to 50% winrate. But the toxic kit that will always annoy you because she has an answer to everything will still be there. So what we end up with then is just bad design.
You can compare it to giving lux a passive that keeps people at a distance from her. That would make her insanely broken, so over time you nerf her damage until she is back at 50% winrate. Now ask yourself would it be fun to play vs that lux? She has a answer for everything, for every situation. Its quite interesting to see that when riot designs a champion they only focus on how you feel while playing the champion. They apparently put no thought at all into how it feels to play against it. And thats kind of weird.. for every person that plays irelia, 5 people have to play against it. So making sure that a champion does not have a kit that is to frustrating to play against is pretty important. Riot has not yet understood this and its really weird, the result of that is what you can now see in the new and improved irelia.
They have some sort of issue with giving a champ a thing/situation they are bad at/in and then just leaving it at that. Make new squishy evelyn? Make her very vulnerable if she gets caught? give her an ult that instantly gets her out. and thats why evelyns ult is so weird, as you will pretty much always teleport out with it and not in, like most other champs. Its specifically designed to make her weakness irrelevant. Yasuo has two spellshields, one placeable, one that only works on him, if he does not need it he gets more damage, no choice you have to commit to and decide before you engage. it just gives you what you first need. he has a spamable spell that deals high damage and is a skillshot so you can get it off even on champs that are out of range of aa or is invisible. He is ad, so he also has high sustained damage. he is meele, so he has enough mobility to make that fact irrelevant. he has cc on a long skillshot, but he can choose to also make it a wider aoe that is targeted. his ult also disables enemy until he has done his damage. I dont care that he is 50% winrate, this is incredibly bad and frustrating design. and before you think "hard cc that is targeted in addition to enough damage to burst him down does counter him".. that counters literally every single champion in league, its like saying "killing yasuo counters yasuo". This is the new league of legends.