It is an experiment, one conducted by Blizzard ot see if htey can actually manage to reintroduce RPG elements that the players claim to want without having everyone whine and complain.
Being able to choose whatever is nice and all on a surface level, but with it comes the ugly truth of swapping builds for every occassion instead of either diversifying or risking it on a specific build.
Convenience is in many ways antithetical to a fully realized RPG world. And in the case of WoW the amount of convenience has clearly gone too far, which looks good when all you want to do is go straight to your raid, but less so when you want to immerse yourself in a living breathing world of adventure.