So, I played some more games recently, with and against Irelias...
She actually is OP. As much as I was skeptical, I found out why:
Irelia does physical, magical, and true damage. A mixture of all 3. You cannot itemize against her, the only thing you can hope for is a frozen heart and a randuins, and even that won't stop her at endgame.
She is pretty fucking insane right now, if played correctly, because she chews through anyone she wants, and her innate CC reduction plus merc treads is just grossly effective, especially as a carry.
Also Riot needs to get their shit together, they're 3 days late with the new champ now.
Oh also, building Mundo as a tank and then slapping atmas on him as your very last item is fucking hilarious, because the team will be ignoring you in team fights at that point, but you'll be raping err body in sight as soon as you've got that one item. olol pubstomping.