I've been saying this for a while now.
It all comes down to how dungeons are designed.
When you have 8 dungeons where 6 of them have low-impact 3-4-5 mob trash groups from start to end then obviously mass pulling and/or low CD AoE pumpers are considered S+ (Like Fire Mages, Outlaws, Destros [now], WW etc).
The main issue is that these 8 dungeons will stay the same from the start of the expac until the end of the expac.
So in the end no tuning will change what is considered "top tier". Numbers might determine the top order but it will always be the same classes/specs.
The only way a new class/spec may emerge if they add a new broken power (like current Destro and Survival).
They should really start looking into designing at least half the dungeons in unique ways. More big mini-bosses, less grouped trash.
Environment that makes it impossible to group large amounts of trash. Things that allow cd based classes to get their big CD's back earlier (low CD classes already don't care, but if big CD based classes get more uptime it might push them forward).
It's all about content design in the end, you can adjust classes any time, but you need the content to be ever-green.