I'd swear there was a position on staff for someone to oversee dev activity. This makes at least two public shows of ineffectiveness of that position. Don't take this as criticism of anyone, just take it for what it's worth - a suggestion to consolidate some policies and communication behind the scenes.
This post is not to beat up the devs or supervisory staff. That's my disclaimer. This post is also really long and for that I apologize.
A long, long time ago, I applied to become a dev and my application was accepted. Following a crash course in how to use the developer utilities and cutting my teeth on designing a quest (the now infamous "awful fairy", itself the subject of a nerf or two), the other devs in my class of dev trainees were assigned to populate a very large outdoor zone with quests, mobs, raid mobs and events.
There was a thread in the dev forums for us to coordinate, and we had each other's emails and whatever else. Basically what happened was that we ended up splitting the zone up by quadrants and cool geographical features and then going to work with our ideas, which basically were fleshed out in a couple of lines in a post and then acted upon.
I felt (and I think other devs in my group may have felt the same way) that our mission was hopelessly vague and that feedback was very hard to come by. The dev staff was always available to give us programming pointers, but not much was available in the way of guidelines like "don't make mobs that charm and blind, nobody likes that" or "don't put spell x on item y". Slaariel lurked around to make sure we didn't commit any misconduct offenses. Slaariel you're my bro so don't take this the wrong way ok!
Anyway, after making a really cool event with Rari (who did most of it as I recall and was a pleasure to work with), the magnitude of dealing with a giant zone with no direction between 4 people crushed my hopes of being a dev. Some time later I resigned because I felt like I was adding to a patchwork quilt and not creating some cohesive picture.
As for the real devs, they get less supervision than that. They work in secrecy, even from each other, and generally are so busy that they never check out each others' work. They may not be allowed to, either. Basically, everybody just makes their thing and then you mush it all together in the game world. That's why tomes feel the way they do, and sometimes overpowered mechanics emerge where two worlds of thinking meet. Or why zaela seems so surprised when someone does XYZ to LMNOP.
This is also why rewards differ so greatly between pieces of content. Some devs are stingy with rewards. Others subscribe to the "Monty Haul" DM theory (for those nerds amongst ye who play Dungeons and Dragons). This lack of cohesion makes it so balance in the gameworld is tenuous and basically impossible to achieve.
Add to that the continuous rebalancing threads and differing opinions on how things work and/or should work - that's the formula for the sands of time-dollars falling through the hourglass of nerdfingers.
edit: the final bit that I wanted to add is that none of the content devs actually play the game. They played before, but none of them have time to play and dev. They are also prohibited from doing their own content for a certain period of time after it comes out. Those factors mean that no devs are play-testing their own content or even each others'. In this way, unbalanced items or encounters will never be discovered unless they have been in the wild for a long, long time.