AP mages are straight out unplayable this season.
Their required itemization is way too expensive and has been gutted. Meanwhile the itemization that counters them has been massively buffed. The fact that they can be totally invalidated by a 1300 gold item that gives damage is just sad. To back up my claims here is some champion winrates: Viktor: 44.5% Veigar: 44.8% Cassiopeia: 45.7% Syndra: 45.8% Orianna: 45.9%
The only mage with a good winrate is lux, but that is because she is very simple to play and people still don't know how to play against her.
A suggestion to fix this tragedy is to revert the gutting of mage items on patch 5.22. Before that evil patch, mages were in a decent spot.