That was Season 1 and 2. We are now on Season 7. Disregarding the 5 seasons in between, AP values have gone down considerably. Zhonya's was split into two items. The AP on Hourglass was then reduced. Blue Buff lost the AP % increase, and items like Rylai's and Banner have lost AP as well.
Banner didn't exist in seasons 1 and 2 and is actually an example of more damage from items that didn't used to exist.
From patch 1.0.0.152, the patch that Ryalis was on and balanced for over 4 and a half years to now, it's lost exactly 5 ap. Whoopdiefuckingdo. Yeah, it lost 25 AP from after they buffed it up 20. . . but remember they buffed it up 20 ap first, when they buffed the AP on a lot of defensive and niche AP items so that they could off set the AP removed in other places.
Mages were doing too much damage with the extra damage given to them in their kits (something you didn't comment on, the fact that these mage support are all failed midlane mage reworks should tell you something). RIOT gave them ridiculous free damage to stack with the increased damage on items and the increased damage from runes.
Let's look at Brand for a solid example of this. His passive, if he hits 3 stacks, is a massive AoE %max hp magic damage nuke that usually is a third to half his damage and scales in two ways so he doesn't need AP for it to hurt as it naturally scales already off his opponents stats. Yet, more AP and more magic pen will make it hit harder so Brand usually opts for the extra damage on items like Liandry's and Luden's Echo, and the DFT mastery which add ridiculous damage coupled with his passive reapplying it and Liandry's, then gets sorc shoes so he can abuses high base damage and skills that scale off his enemies stats, while also removing 30 magic resist +runes/masteries so he can do true damage to a ranged ADC without mr items. Oh, and he has a hard CC to enable his combos and help his ADC get off more damage. He's actually is able to do more damage than previously despite lower AP by abusing itemization, and the new masteries.
Malzahar similarly has a strong AoE % max hp magic damage nuke, but his also hard CC's his target during said nuke enabling his ADC likewise to pump out more damage. Oh, but of course, most of his damage is from voidlings, high base damage low AP scaling so hey, he isn't hurt by lower AP scalings and still dumpsters people as a support to the point where he can often 1 v 1 junglers or solo laners later in the game, or if he can get off a full combo. He also abuses magic pen, being able to constantly reapply DoTs and damage instances to keep DFT and Liandry's on targets as much as possible.
Zyra, same basic shtick, except much more sources of high base low scaling magic damage from all her plants, still does the magic pen, liandry's DFT thing, and still does ridiculous damage. Trades in % max hp magic damage for higher bases and AoE hard CC on two abilities.
Regarding masteries and keystones, Riot has already toned down the offensive outliers, reworked the sustain Warlord's gives, and reduced the AD scaling on DFT. In terms of how you could put 18 into resolve and still have more offensive increase than if you had put your points into Offensive, that's simply not true.
Perhaps I wasn't clear, assuming you are referring to this passage, "remember, the old 3% increased damage at the end of the offensive tree that these champions could never effectively afford to get? Now we get that so much earlier and have so much more % increased damage, someone getting a keystone in resolve, and only using 12 points in a different tree, either of them works, will gets more increased damage than someone investing 21 into offense in previous mastery systems" be careful to understand what I am talking about.
I am comparing the current trees to the trees that existed in previous season, specifically this tree from season 5, that was replaces with the abomination, keystone bullshit we've been forced to use for the last year and a half, and which is slowly rotting the game from the inside out. The old "keystone" --if you can call it that, the single end point of each tree that you needed to spend 20 points in said tree to unlock-- for the offensive tree was called Havoc, "Havoc: Increases damage dealt by 3%."
That was the end of the offensive tree, the reason you put 21 points into it. 3% increased damage. Going Assassin and Merciless in cunning takes only 11 points and is potentially a 5% (previously 7%) increase in damage, so yes, you can go 18 into resolve, and still get more damage amplification with your remaining points than used to exist in the entire offensive tree.
Wanna go a step further? The defensive tree used to offer reduced damage from AoE, from critical strikes, from every instance of damage, it gave a potential 22 armor and magic resist + 4% of whichever was higher as the lower resist, and then increase both armor and magic resist by a further 10% while also granting 3% increased maximum health to counter the damage increase from Havoc, and also gave regen equal to 1% of missing hp constantly. The resistance masteries actually triple dipped into eachother, and when added to the flat hp and 3% increased hp actually gave a metric fuckton of increased ehp. At minimum it gave 1.22x((HP+36)x1.03) increased EHP. At 1k hp, it gave 1300 increased EHP, at 3k hp it gave 3,815 increased EHP, oh, and 1% of your total EHP per second is returned.
The neutered the defensive tree to the point where only a few nodes actually increase your fucking defense (as the tree is half utility, now and often that utility such as Insight is so fucking good compared to the defensive choice it competes against that it wins out literally 95 times out of 100) while throwing damage increases and damage dealing keystones at everything. Hell, even Grasps of the Undying had to be nerfed multiple times because the defensive tree keystone was doing game-warping amounts of damage in laning, just to give you a clue how fucked up the system is.
