The raw ap has been reduced?
Only because AA isn't the go to anymore, which it was in S1 cause of the lack of other options and the generally more lategame focused meta.
With AA, roa, raba, void and morelos, you still reach similar numbers to S1/S2, especially with stuff like fire dragons and bluebuff(Untill now that is)
AA gave only 45AP on top of the mana->ap conversion back in S1, now it's 80, that's 35more
Morello's didn't even exist in S1(or if, then it was released at some point in S1), and at release it had 15%cdr and only 75AP, which is 25less than now
RoA used to give 80Ap fully stacked, which is 20 less than now, but 630hp(increased to 650 in S2) instead of 500, so more tankiness
Rylais used to give 80 ap and 500hp, compared to prenerf 100 ap, and while it's slightly more ap than the current nerfed version, it also gave nearly twice the hp
Voidstaff gave 70 rather than 80AP
DFG back then gave 60AP, later 80, though it had an absurd active
When we had Zhonya's ring, giving 120 AP and 25%AP compared to rabbadons 120AP and 35%
On top of that, no Ludens proc, no Liandriels(and thus no lategame flatpen item), no Keystones.
The equivalent to keystones back then gave 4% increased damage - thats less than the tier 4 ferocity masteries give!
So actually, not a single item in S1 had more AP than it has now(had in S6)!!
What you guys think of is S3/S4 with the big 120 AP items.
Also, regarding to your previous statement:
Mages has had base powers of 280-320 on basic abilities(...) AP ratios were usually ranging from .8 to 1
Yes, the base damage were quite high, but so were the CDs. Yes, this means the burst was there, but not the dps.
Also, if we take a look at some newer champs:
Thalia : Q does 420+1.2 if it fully hits, E hits for 0ver 300+ ~1.0AP(to lazy to calculate the exact value right now), and on top of that she has her W for 140+0.4, while many of the champs with 300+ base and 0-8-1.0ap ratio in S1 only had two damageing skills.
reworked Victor: Q does 343(inclueding his base ad on the AA) +0.9ap, his E does 410+1.2ap
Syndra: Q 230+0.75 on 4sec cd, W 240+0.8, E 250+0.5, so the base kit ads to a total of 720+2.05ap, compared to let's say S1 Sion with 320+1.0 on Q and 300+1,0 on E for 620+2.0 total, just with huge CDs and without ult, or Malz with 620+1.6ap from q+e and some %health if people stayed in W
Also, for half the never mages it's really hard to compare, as their damage isn't delivert in clear burst rotations.
Aurelions values look low on paper, but the consistant damage of his passive/W adds up to massive damage, same with Azir and his soldiers or Zyra and her plants.
just be "Let me press R for 1k AoE damage to everyone and hope the 
