The solution is pretty easy. All DPS specs have about the same DPS potential and scaling. If a class doesn't provide buffs, then its DPS is a tiny bit higher (say 5% max). Though personally I think all classes should provide good raid buffs and/or debuffs. Rogues perhaps could be a debuff-only class, I suppose, though a they could easily enough have a few buffs too. That would be a change for them, but far from problematic.

Remember that fine-tuning damage is going to be one of the last things they do for the classes in beta.

Anyhow, things don't have to be perfectly balanced, getting damage within 1 or 2% (assuming the same skill level) is good enough. Heck, even making skill being the main factor in DPS output (among DPS specs of all classes) would be quite sufficient for most people. They seem to be planning on doing some of column A and some of column B here, which is good stuff. Perfect balance? No, but close enough for 99.9% of the WoW community.

"Remember that fine-tuning damage is going to be one of the last things they do for the classes in beta."

Or, something they don't do until 6 months after the expansion goes live, as was the case with mages last time around.

To be fair, they do seem to learn from their mistakes, and they know mages need a lot of work in this area. Hopefully we won't see a repeat of BC problems.