I agree with you that having a tanky mage is VERY toxic, but in it's current state AP itemization is just worse than AD in almost every way
Having some sort of battle mage item focused around helping immobile mages fight back against highly mobile assassins that can build slightly tankier or have some form or reposition, Master yi with rageblade and full tank can generally dive a mage and take them out or die with them, having an AP version of maw (gives a small shield and slightly increased armor+ap) would help immobile mages survive in a harsh environment, it could even have a longer cooldown than maw
I probably won't leave any more responses but I feel that mages could use an AP version of maw that gives SITUATIONAL tankiness instead of actual permanent armor and health, thx for debating and sharing your opinion [slayer-pantheon-thumbs]