I understand that most warriors just killed mages in the stun.
Some warriors actually did cancel spell casts by running through a toon. Where was that EVER intended? The cast has an initial facing requirement and a cast time and it requires you to stand still. All three of those. It could have a cast and allow movement or it could be instant but not while moving. Cast time spells have many limitations... also, including pushback.
The last thing cast time spells needed was to be vulnerable to being canceled by running through a toon.
No the guys strafing you is NOT doing this. All you have to do is NOT keyboard turn to counter this. You have NOTHING to counter canceling a cast running through you except for to pray the warriors timing is bad, or to NOT cast cast-time spells at all in melee, or to pray they don't know its possible.