I think the trap a lot of people get into is trying to be optimal in this bracket. The norm for wow, and a lot of brackets is that we all want to have bis gear, on the bis race, in the bis spec of the bis class, on the bis guild on the bis realm. This is simply not necessary for this bracket.
You got to remember that this is the f2p bracket you're talking about. If you're playing pugs, then just about everything is "viable" as a 29, that is, you're at least as viable as what a f2p would consider viable, which I think is the meaningful definition, unless you are seriously into scheduling 10v10 premades (never going to happen) or wargames against other 29s.
My definition of viable is the ability to be valuable in some way to your team, or achieve some kind of goal for yourself. Like in my above post, my goal would be to cc people, with the sole purpose to annoy. Mage can always going to succeed at this goal, with one ability, even if they couldn't kill anything. But mages can kill lots of things. A f2p arcane mage can burst down many classes, f2p or 29s, if they can get some heals, or just play it right. I can't imagine a 29 mage would be somehow less viable.
Just because something isn't tops in damage or heals doesn't mean it's not viable, especially when it comes to locks and mages, because they have abilities that can take players out of the equation for x amount of time. Opponent's time spent in cc would be an interesting stat for the scoreboard. It would be like powerplay minutes in hockey, and would help encourage people to use their buttons (damage mitigated would be another one, but that's another story).
Anyway, my opinion is that the f2p bracket is different than other brackets because as a pugger, you don't really have to take things as seriously as a 29 because you're going to be in a good position to succeed at your goals whatever you do. This gives you the ability to do silly things, and play non-optimally if you want to. You can play undead for every class, even if it isn't bis race because you've got plenty of overhead to work with, but it gives you the ability to eat your opponent, which is winning. So you get one shot by a feral? Whatever, feral deaths don't count; rez and repeat.