Old Irelia wasn't bombarding your screen with Es and R and having ridiculous base damages. Her windowed power gave you far more time to handle her, especially in lane, compared to her no-downtime new passive that stays up for as long as she's touching you, which on top of her much-improved burst potential (IMO the real problem of the rework, nice 500 base damage on her R and spammable Q) is just a little too much killing power. Yeah, the old stun was annoying, but it was entirely a numbers issue and could be tweaked many different ways. Old Irelia was slippery through tenacity when outnumbered; new Irelia is just as slippery without the condition thanks to Q resets while also having a huge % DR soak as an emergency button. You can't really address new Irelia's issues with numbers changes, you'd have to start taking stuff out of her kit and I think we're going to keep seeing Irelia on the patch notes until Riot realizes this.
Also it doesn't help that her 2 skillshots are so ridiculously wide, especially her E which can stun you at least 3x as thick as the visual indicator might actually suggest. This isn't really a design flaw but it's certainly a massive headache.