I am MT for my guild, and did not respec out of prot for my 5v5 arena fights.
We had a holy priest, holy paladin, rogue (unsure of spec), enhancement shaman and myself, 5/11/45.
I expected going in to be little more than an annoyance, one that bad teams (if we were lucky) would focus on and one that good teams would ignore. What I found instead was that between pummel, conc blow, pummel, war stop, pummel, intim shout, pummel, intercept, pummel, I was able to keep a healer locked down for a very long period of time. If a team had two healers, I went for the heavier one (pally or shaman) while the rest of the team focused on the ligher one (priest or druid.) We went 13-5, raising our overall rating for the week to 1590.
Add in Commanding shout, intervene (yes, common abilities, I know) and piercing howl, and I felt like I was contributing a lot, and had reached the realm of "utility," up from "annoyance."
I wore duel wield DPS gear to help with rage gen, ready to swap on a shield if I attracted magical DPS attention.
Would a DPS warrior been better suited to my spot? Perhaps. They don't have as many interrupt options, but have additional damage available. Did any of my team feel like I was a waste of a spot, even though we all half expected/feared just that? Nope.
Not to rag on you, but the only difference between you and the arms or fury warrior is neither of them have concussion blow, which still has a 45 second cooldown, otherwise the interrupt options are identical. The former would have Mortal Strike though, the latter would have the option of Improved Intercept which I found to be a really great PVP talent when I did PVP, and Death Wish does have varying utility just from the fear prevention. Both have significantly higher damage output too, and that matters, because it forces their healers to actually have to deal with someones face getting stomped in. Again, the Protection warrior only has 1 additional stun, really poor burst and sustained damage output. Compared to other classes who can heal, stun, or otherwise have more reliable CC options, and significantly higher damage output, the Protection warrior really has no place on a serious arena team. Sure you might be a quick distraction but honestly a good team would recognize that you really aren't a threat pretty quickly, cc you off and focus fire the actual threats on the team.
I guess there is Shield Slam, but I am not convinced its in fact a 50% dispel, more like 10% if that for the times when I've used it and it actually dispelled anything.