Since the launch of the Battle for Azeroth pre-patch content in World of Warcraft, players have been loudly complaining about leveling changes and the length of time it has been taking for players to move from one level to the next. Blizzard's Ion Hazzikostas has gone on record as saying that, yest, something changed to make leveling much, much slower than before the update, but that the team is having trouble tracking down exactly where the problem lies.
We "squished" stats and item levels, but this was done with the aim of being neutral with respect to the duration and lethality of combat. When we heard complaints about things taking too long to kill, we immediately assumed we'd gotten those calculations wrong. But a look at the raw data didn't suggest any clear anomalies.
We are seeing the same sort of discrepancies that folks in this thread and others have pointed out, but still have yet to pinpoint the exact aspect of scaling that we failed to account for. We want to understand WHY the numbers are off and fix the underlying cause: Were stats on gear reduced too much? Some aspect of creature armor or other combat calculations? Are our baseline values accurate, but the shape of the scaling curve wrong such that it’s particularly far off the mark in the 60-80 range? We would prefer a targeted solution versus just applying a bandaid fix that could mask deeper issues that could cause problems down the line, but at some point it’s not fair to give you a degraded experience for the sake of that investigation, so we’ll likely go ahead with a blanket health reduction in the near future while we continue to investigate.
In addition, the leveling experience between 60-80 has been a sore spot with the community since patch 7.3.5. The feeling from the community is that those 20 levels are excruciatingly slow (and they are), particularly in light of the fact that many players are leveling up new characters from the Allied Races in order to obtain the racial "heritage armor".
Hazzikostas admits that this is a big issue, with players in that range taking about 15% longer to level than in the range before 60 and after 80. They will be applying a "set of changes that will smooth out the experience curve at level 60 and beyond, reducing the experience requirements for those levels".
You can read the full post on the World of Warcraft forum.