My point is that I could (and have/ max out Fire and 'specialize' in aoe, but that still makes me really bad at single target so I'm still required to max out Frost.
Then at any point Blizzard could decide Arcane is the best spec and then that ride starts all over again, especially in 7.2.
If you're in a strong guild who's likely not going to get stuck till like, Elisande or Gul'dan you could argue to just go with the spec that works for those bosses, but mages don't really have that luxury as frost is much better for Augur for example which you're likely getting stuck on as a slower progressing guild.
Anyways I'm tired and ranting while not being very coherent, my point is that AP sucks for classes with multiple dps that are all good for different bosses.