While I respect your opinion I have to agree with Blizzard's current philosophy. Even with dual specs I think it is important for each character to at least have a few different styles for pve and pvp content. Much like warriors have a pve dps spec and a pve tank spec i like that they have a pvp spec besides arms.
As arms you're mainly a peel and ms'ing but with prot you're more focused around utility such as reflecting spells at crucial times off your teammates, locking down healers, and using your mobility to harass multiple enemies. Your job all of a sudden anymore isn't about making sure the ms debuff is on and when the best time to use bladestorm is. That's what i like most about pvp'ing as prot. jigslol posted a great vid of his ATC team and he displays this style very well in his video "Protin' on nerds" (no accounting for taste on the name).
But all in all I do not agree with the op i think prot pvp in cata will be strong especially rated bg's. The only thing that i would like back is the imp spell reflect talent in the form of a major or even prime glyph.