The skillup adjustment firstly targets low skill levels. The rate at which you can skill up a particular skill is unbelievably high at low levels and tapers off to be more or less near what it was before. The fact that you can cap skills on DC mobs (which I believe is as low as 82 or 83 to a 90 player) is the biggest advantage to high level players. I've done a decent amount of leveling since the update on very low level jobs and found that I could recap my primary offensive skills after leveling on just 1 to 3 mobs because I'd get a skill up on nearly every single hit. My only level 90 job (BLM) already had all magic capped, but I have been able to skill up staff and club a bit. It's hard to say if the rate is particularly increased given the frequency of their use.