In a broad range of gaming genres (from RTS to Action RPG), being able to zoom out and see more of the world around you provides an objective advantage in the form of information. Due to that competitive advantage, camera-unlocking or increased zoom distance are features commonly found in third-party hacks for a variety of games. Whatever the maximum allowed, that's what competitive players will use in order to maximize performance, even at the expense of the game's overall look and feel.
We strongly believe that there needs to be parity in this area between players who are using the default UI and those who have addons or knowledge of hidden console variables. One option was certainly to just allow the in-game slider to go all the way up to the CVar hardcap. But that scale is beyond the one around which the game was designed at its core. The development team builds the world, its art, its combat mechanics, and other interactions, around the base UI experience and scale. At the 3.4-CVar zoom level, your heroic Warcraft avatar takes up about as much screen-space as one of the dozens of marines you might control in a game of Starcraft.
Basically all of us started out playing WoW at the UI-enabled zoom level, and fell in love with that world enough that we now find ourselves here posting on an expansion beta forum discussing its future. At some point, we saw a raid video and wondered how they could see so much of the field at once, or we saw a forum post or got a helpful tip from another player, and learned that if you typed "/console CameraDistanceMaxFactor 4" you could zoom out way more, and we never looked back. But was that original experience bad, or have we just grown accustomed to something different?
There may also be a bit of hyperbole in the discussion around the change. This is a screenshot I just took with the max UI-selectable zoom settings in the current Legion build: http://i.imgur.com/e8vFT6t.jpg
I'm not sure it's fair to say that this level of zoom entails your character dominating the screen, or removes all awareness of nearby threats.
Finally, why did this happen suddenly now, late in the beta cycle, seemingly without any communication? Honestly, the intent was for the change to have been in place from early alpha onwards. I believe that what happened was that one of the CVars (CameraDistanceMaxFactor?) was clamped from the start, but a second CVar (CameraDistanceMax?) was overlooked. That issue was entered and tracked as a bug, and was just fixed recently. As a development team, at this point we're fixing up to 2000 Legion bugs a week, and it's not always obvious which player-facing build will contain a particular one of those fixes. This clearly wasn't something we ever imagined could just be swept under the carpet.