Is Sheen a really good item or is Irelia just broken(more so than usual)

Whenever I play vs an Irelia or someone else does I noticed they usually stomp her face in hard, but once she gets sheen she suddenly hits does a crap ton more damage.

I like Irelia and i've played her a bit before in the past, I'm almost certain she didn't have and still doesn't have some type of damage steroid (unless you count the true damage)

I've seen ezreals/corki/lucian etc. get Sheen and not hit a power spike as hard as she does