alast Irelia does not have a armor/MR, shield or % damage reduction so that stun is her defencive ability.
It is not guarantied to be a stun where as otehr champs like Maokai get a 2 second reliable root on top of 20% damage reduction.
I am assuming it is the factor of you think you are winning a trade in top and then you get stunned and lose that is making you frustrated. You often times do not have to trade and that is something that might sound hard to do but often in your best interest. Unless you are already at a huge disadvantage and the enemy can dive you without worrying.
Riot has said they plan to rework Irelia since as long as I have been playing but clearly she is not that big of a problem considering some champs who came out after he already got a rework.
Nerf Fiora and Irelia appears as your target of frustration. Nerf Irelia and divers in general and you suddenly have all tanks being played top. The cycle continues.