2 things:
1)
i would not expect that differentiated and deep, well-thought oppinions on mmoc
i wait for the obvious "if you just play normal/HC spec dont matter" statement
2)
dont forget that specs are relatively close togehter this xpac (and even more this tier), so the fact "how good you can play fire/frost/arcane?" matters even more. if 1 spec is YOUR spec, and you can perform it like hell, this will instant close the natural dps gaps between the the 3 specs. same goes for "you cant be very good at a spec you dont like". so, my advise is: analyze a lot, but test a lot more. play what "flows into your fingers" and what you like. and you will perform better than spec xyz, even when this spec have more space to grow.
oh, and think about your playground: you dont play mythics. and maybe play pugs. so you have
- a lot of randoms
- a lot of stupids
- way more short living adds than long living (important difference berween many specs)
- not straight moments of raid lead yells "now xyz"
- more "play for your own" than "play for the group"
- no time-ahead planing like in guild that do every encounter exact the same
- and so on