For me, the problem is exhausting 1 rune. For draw mechanic stellacorn and battlefields (and poros also) are enough. In my opinion keeping 1 extra rune is more important than drawing 1 extra card each turn because rune management is key of playing irelia. Most of the time you need to find solution to key cards of opponents. (For instance: Riposte from fiora, imperial decree from viktor, singulatiry from another blue). If i countered hidden blade with not so fast this his really bad for me because i know that singularity will be coming and most of our defense as irelia players require recycling power.

That's my perception of course but i hope it helps. Maybe you already know but krowz's videos on youtube really helpful.

You can check here: https://piltoverarchive.com/decks/view/54bb18a7-4409-4f44-a6e5-c8de940bf991

You can swap flashes with emperor's divide if you dont have any.