AP casters damage overly nerfed or OK ?

I can't remember when AP casters ever would be doing so little damage as they do now since new season started. Is there any chart to compare overall AD damage output vs AP damage output ? Maybe it just me, but somehow it feels like AP going through the worst game balancing since LOL beta.

I am OTP Zilean. Zilean haven't been rebalanced since he was changed years ago, meanwhile LOL roster got tons of gap closers and damage denying champs which makes Zil in the worse situation to when he was changed. Not even that, Zilean gets significant indirect nerf due to AP items nerf.

ps. I am missing the meta we used to have 2012-13. Those were glorious days of LOL.