Illucia will be broken but there is a difference between a hard counter and auto-win.
Hard counter means you can try to play the game actually because you can win maybe a 1/3 of matches depending on your approach/threat assessment/resource management/etc. auto-win means if you queue up against it press concede is faster than wasting 20 min to discover you lost from the beginning...
I'm not against hard counters if something hard counter other deck so beat it, but Quest Mage is the actual problem in wild go watch Zeddy and he has videos telling the data from High tier wild/low tier wild / mid-tier wild and everything is either Quest Mage beater or Quest mage so I'm happy for Illucia coming around cuz if that means both mages get to play they crazy stuff a little more and I can beat that shit sometimes I'll very happy about it.
The priest still doesn't have a good draw engine compared to others so a combo deck can still win against. ( and that will be a hard counter btw )