Prot is pretty strong right now. I don't think it's stronger than arms, except in 1 comp, and in duels. Arms warriors have always lost duels to almost any equally skilled/geared opponent though, I don't see why that's an issue when they're so strong in group play.
Also, the US TR top 8 was
1. TSG 2. Beastcleave 3. LSD 4. MLD 5. Ele/Shadow/Rdruid 6. WLD 7. MLS 8. Hunter/Lock/Druid.
TSG actually had 2 teams in the top 8, but obviously they can only take up 1 spot at regionals. It looks like the #3 LSD and the #7 MLS probably won't go to regionals either, and will probably be replaced by an RLS and another beastcleave. So the top 8 was slightly caster heavy, although much more diverse than the EU top 8; and regionals will likely be actually fairly even, between melee teams (TSG, beastcleaves) and caster teams (MLD/Talbadar's team) and balanced teams (WLD, HLD, RLS).
That said, balancing pvp around what the very best players in the world are capable of when given the very best gear is a horrible design decision. The high end arena population is less than 1% of people who play the game.