Irelia nerfs are a joke.
-5 ms doesn't change the fact that she is has the most deadly all in in the game past level 2, and is ridiculously snowbally that getting behind in lane invites her to one shot your top/mid laner under his turret. As soon as she's extremely fed, either due to the fact that she's killed her lane opponent over and over under turret constantly or now has a super high gold lead because they were forced to play super safe the entire laning phase, you can't deal with her mid to late game because she one shots you while simultaneously being a nearly invincible tank.
I would seriously rather go against a full team of Sion, Graves, Akali, Kai'Sa, and Pyke than play ANY game where Irelia is on the enemy team. Fuck this champion.

all broken as shit.
now give less MS
ganks are harder to run from
support speed ups are weaker
Yasuo was hit with the same, and got reverted because it was too heavy.
Same issue with lee sin. His ganking power and win rate dropped heavily after he got -5 less MS.