Gameplay-wise pretty much every melee auto-attack bruiser is a design disaster and the only ones with real counterplay (Yasuo, Fiora) are despised by the community even more than the ball of stat alternatives (Irelia, Jax)
You're confusing counterplay and outplay potential.
Counterplay is the ability of your team to react appropriately to a character, it's often not individual and is normally strategical rather than mechanical. This is often stratagies such as picking on a weak early game or forcing a champ who can't splitpush into a splitpush scenario. Irelia and Jax have far more counterplay than Fiora and Yasuo.
Outplay potential is the ability to beat a champ with mechanical proficiency. This isn't actually counterplay as when the champion plays well you cannot outplay them. High outplay actually correlates to low counterplay, champs like Zed, Lee and Fiora actually don't have high counterplay because your only option to play against them is to be a better player, you can't pick on strategical weaknesses because these champs are just too well rounded and can play too many strategical roles.
I'd also argue Yas and especially Fiora aren't AA based. Yas's damage is as much from his Q as his AAs and Fiora is heavily reliant on her Q. I'd consider them both to be hybrid AA/Casters.
She'd be much, much more likely to succeed as an AD caster because that design is inherently less offensive.
Is it? Last I checked people often complain about champs like Riven, Lee Sin, Renekton, GP and Darius when they're strong. All of these champs are more casters than AAers.
Overall I think that Irelia as a character was never a good fit for the type of champion you want her to be. She'll always be at odds with her character if she's based on autos.
It's better for Irelia to be at odds with her theme than at odds with her player base. The simple fact is that Irelia players enjoy her as an auto attack based bruiser, you can't just ignore that when suggesting rework ideas.
You're a Sona main so I'll put this in a way you can understand. It's kind of like if the community started saying Sona should be balanced around being a midlaner. From a mechanical standpoint it makes sense, Sona's current kit is closer to a strong fit for mid than support, if her Q had an AOE splash ala Karma so she could wave control she'd be a pretty good mid and they'd be reasons to pick her which are currently somewhat lacking.
It's also a complete bastardisation of what Sona should be. In my case I'm bastardising Sona from a thematical standpoint while being consistent in a mechanical standpoint (she still plays the exact same), you're bastardising Irelia from mechanical standpoint (she plays completely differently) whilst being fair from a thematical standpoint. Both of these are terrible for the players of the champ.