When I left EQ for the first time, AAs were based on level 51. Meaning if you set your AA/Regular Experience Bar at 50% at level 51, you would gain AA Experience and Level Experience at the same rate. However, when I first turned level 51 on this toon, I set my AA/Experience bar at 30% to AA Experience. I still gained AA experience much more quickly than regular experience. So, what level is AA Experience based upon now?
No one knows, but it is hard coded that you can't get more than 5AA per kill even with XP potions. At L115 I get 0.05% XP per kill while getting 1-1.5AA per kills. All live servers have auto-grant enabled, so you get everything 5 expansions old. Right now, in ToV era, you get every AA through TBM autogranted just by clicking the box. This means you receive about 15000 AA for free. There are still another 20000 to purchase.
There is also the bonus AA rate for AA manually earned up to the first 4000. So that will affect the rate by bumping it 10% per kill. After the 4000 then you would only earn them at a flat %. You lose that bonus if you Auto Grant. Many players can get 6-12 AA per HA around level 90 ish. But that is mission based not kill based. I had never heard of AA being based on level 51 but you do start earning them at level 51 except for Origin which you get at level 5.
Back in the day, an AA point was a fixed amount of experience, equal to the amount of XP required to go from 51-52. So if it was 3 million XP to get 51-52, it would take 3 million XP to earn an AA point, no matter what level you were. Obviously, this was much easier to do at 60/65 than at 51, so most people didn't do AAs until max level. For the most part, this did not cause too many issues during Luclin, and even PoP, and worked fairly well at the time. However, fast forward ~X years, and the level cap is now ~90 or something similar. It was getting to the point that mob health (and therefore xp per mob) had become so inflated, that level-capped players fighting high level content were getting an AA point every single kill. This also made a "Get to max level, THEN AA afterwards" mind-set the norm. As a result, you were getting Level 75-80 characters trying to tank level appropriate content with ZERO AAs. Both these factors contributed to how the system is now (which very few people know exactly how it is calculated), but it does have the benefit of people being able to stop at certain sweet-spots and push out 100-200 AAs without feeling it is the "wrong" time to do so.
As I understand it, one AA requires the same amount of XP as it always has, but what they did was cap the maximum number of AA you could earn per kill.
