What you quoted has nothing to do with your concern. The quote was about trying to hide plot points from players, not changing content based on player feedback during beta testing or other public testing (they tend to fail at hiding the plot points, regardless). Blizzard doesn't make changes to content based on tester feedback once development moves out of alpha and into beta. The most you see are some changes made shortly after beta testing begins that weren't ready to be implemented before alpha ended.

If you knew anything about the history of WoW beta testing, you'd know that opening FFXIV beta testing to players would not achieve the result you're looking for. WoW is notorious for ignoring tester feedback even when most of the time the feedback is spot on for predicting how the player base will react after release.

The other thing you're conveniently ignoring is something you pointed out yourself - not everyone plays the same way or for the same reasons. Making changes to please one segment of the player base is going to upset other segments.

Any game developer ultimately needs to stick to their vision for their content design. Games would be a mess if they were constantly messing with things trying to please a player base that's not in agreement about what they like and what the game should be.