Your preference for a certain stage of WoW does not equate objective perfection for what WoW should be, nor does your enjoyment of the game & its classes remaining the same forever mean that all or even most players feel likewise.
People need to stop looking at MMOs like console games. Things in the game are meant to change. They are not meant to play the same whenever you pop them in to play or to log on.
As far as BC & Wrath being perfect I think that's a laugh. You must not have mained an ele shaman during either of those expansions. Picture what ele shamans were before the on the move LB, but with much less survivability, fewer utility options, no real burst. Basically a useless spec overall. An expansion with utterly trash specs that serve no end game purpose and painful leveling process is a bad expansion in that aspect. Even BC to Wrath was very different and not comparable. As I mentioned earlier BM went from about an 18 second BW/TBW with CC breaking & immunity to 10 seconds on top of a damage reduction. BC and Wrath simply aren't comparable so your statement of them being perfect despite comparatively different is boggling.