Mage items need nerfs (speaking as someone who mostly plays mages)
Even I agree ap itemization is way overtuned right now. You get 33 flat pen for 2.6k gold, and it's not like lethality where it only reaches that point at level 18. Mana is a non issue when 
is finished, and it is 99% gold efficient without the cdr or the passive and the fact that the meta mages have very little mana costs to begin with so they can spam spells off cooldown. I suggest the following changes to the worst offenders.
magic pen decreased from 18 to 15
cost increased from 1300 to 1400
ap decreased from 90 to 80, base proc damage changed from 100 to 49-100 based on level
cost increased from 2600 to 2900, hp increased from 300 to 450, ap decreased from 90 to 70 (this is supposed to be a utility item, not a cheap high ap item)
cost increased from 2650 to 2800, magic pen reduced from 40% to 35% (in line with ldr)
cdr removed, ap reduced from 75 to 60, spell shield cooldown reduced from 40s to 30s, now builds out of 
and 
(I wish building 40 mr in lane isn't a waste)
cost increased from 2900 to 3200, cdr removed, ap increased from 75 to 80, armour increased from 45 to 60, now builds from instead of 
line: tribute damage removed
I also think the bruiser itms need nerfs, specifically 
for penetration, unlike AD champs
or 
is a lot harder to kill with defensive boots, and they dont give up anything for it because all the pen is already on their core items.
