This is a video, where I demonstrate the OP'ness of Prot Warriors on low levels in patch 5.2.
The reason for nerfing shield slam in 5.3 is pretty self-explanatory.
"Shield Slam now receives a 50% bonus to attack damage from attack power (down from 100%) for Warriors below level 85.".
Good. If they can do something about (disc) priests too, then I'd be even more happy! WSG is pretty much this at low levels: whichever team has the most disc priests/tanks wins, which is very, very sad. As a 30 rogue, I've got no chance at defeating them.
Yeah, when I was leveling my mage and monk, I was so frustrated to get hit for more than my max hp could handle
But then I rolled a warrior.... Up until at least level 80, I dealt more damage than the whole team all-together in the instances, and one-two shoted everyone on bgs...
I am not sure that this nerf will change a lot by the way, since the main dmg does not come from attack power. Oh well, time will tell
I actually just got through this last weekend with my last character to max out. Low level regular BGs have always been my favorite experience in Warcraft and over the many years I've seen lots of stuff come and go. For now though you are correct that prot warriors and disc. priests are king of the roost. I was a Brewmaster Monk and so I gave the prot warriors a hell of a hard time myself but there's no way you are probably going to survive a team fight with them in it. At every level range I would go in wearing mostly all heirlooms and blues and still could only hit them for between 4-60 damage at any one time.