The following was just posted by Watcher in the NA forums, copying it here for discussion:

If any of the communication thus far, or the lack of visible action, has given the impression that we don't consider the issues raised in this thread and others like it to be a problem, I'd like to emphatically state that nothing could be farther from the truth.

At this point, the feel and pacing of the level-up experience is a top priority for the team. We made deliberate changes to the feel of combat six months ago in 7.3.5, moving away from a world where low-level players (especially with heirlooms) could often kill outdoor enemies in 3-4 seconds, and where dungeon mobs died so quickly that a caster with a long windup might not even get a single spell off. Those changes were controversial at the time, but we stand by them as an improvement to the overall pacing of the game. But we also think that those changes went quite far enough, and have absolutely no desire or intent to continue moving in that direction. Nothing about the pre-patch was deliberately intended to make combat take longer than it did previously.

So why haven't we fixed it yet? Honestly, because we genuinely don't know where exactly the problem lies, and we don't want to make a blind blanket change that actually misses the real source of the problem. That's why much of Ythisens' and others' messages thus far have been asking the community for detailed examples to guide our search.

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. So we started testing empirically: We can run internal 7.3.5 builds, so we set up test characters (e.g. a level 70 wearing appropriate quest gear awarded by quests around that level - Item Level 115 in 7.3.5, Item Level 79 in 8.0.1) and fight outdoor enemies in 7.3.5, and then take the same character in 8.0.1 and fight the same enemies, and compare.

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.

Either way, the current state is not the game experience we intended, and it’s something we will fix.

There is another issue tangentially related to this discussion that I also would like to address: Many feel that it takes too long to level in the 60-80 range in particular, and that the combat pacing issues discussed here are just a piece of that larger problem. We agree – currently players are taking about 15% longer per level, on average, in that range as compared to before 60 or after 80. We’re in the process of assembling a set of changes that will smooth out the experience curve at level 60 and beyond, reducing the experience requirements for those levels.

We’ll have further updates as specific changes roll out, but we’re prioritizing our work on this problem and hoping to get these improvements out to everyone in the coming days.

Leveling nerfed AGAIN in 8.0