I know some Rioters have said its not a great ability because it punishes you for doing well against her...but that's actually not the case at all.
Equilibrium Strike is an interesting ability that forces her to think about her engages if she wants to get that stun. Imagine if they didn't make it slow when you're higher %HP than the opponent; that it always stunned (which is what would have happened if it didn't have two halves). Despite her resets still being there and still being the most interesting part of her kit, she'd basically just be Xin with true damage as far as gameplay. She'd be engaging every time someone's in range, rather than having to add more risk by missing health or not meeting requirements for her best-case scenario, of which she currently has two: Her Q reset, and her E stun.
Just for laughs now, imagine that it slowed 100% of the time instead. She'd have to be an assassin for that to work, which is not a positive or interesting direction for her at all. Any other case she'd be completely and totally underwhelming.
Having to think about how to get to your opponent and achieve that stun in conjunction with her Q, and optimally its reset, is a large part of what people currently enjoy about her current gameplay. Adding more factors for tanks, bruisers, and juggernauts to think about before engaging is a clear way to make them more interesting and less frustrating to play against. Nobody likes being bowled over just because the other guy's stats were high enough.
That said, her E is not perfect by any means. There should be a threshold for the health difference, as even equal health counts as 'higher % health than Irelia' at the moment. Make it 10% difference and it would be much more fitting, thematically, and would also allow something else in her kit to be a tad more potent, as that 'equal hp' stun is a huge strength of her current laning.
I honestly think removing it as a part of her upcoming rework does her, her fans, and the entire League community a huge disservice. More tanky champions should have abilities that are relatively consistent, but not perfectly consistent such as this.
Keep in mind that, if you were to retain her E's effects, Equilibrium Strike does not need to remain her E ability. It could be moved to her R, even, as it has a huge impact for her when she gets it off as a part of an engage. It would be much more fitting as an ult than her current R's impact.
What do you think?