And yet the OP wants Rogue burst damage nerfed.
On rare occurances you can open with ambush. But most often yes you'll open with Garrote.
Talking from RBG exsperience around the 2k level, I'm seeing backstab CRIT Holy paladins, Resto shammys, disc priests even Hunters for around 16-17k WITH FW up. Tanking classes im seeing it crit for sub 7k. Ive seen 5 point eviscerates crit for 7k.
My point is, that unlike the OP's assumption, actual facts, actual experience of dealing out damage as a rogue does not indicate that burst is too high. In fact you might say that that is the reason rogues retain so much utility.
If you want to look at why certain classes do so well in certain arena comps you have to look at class synergy. Disc and Frost have amazing synergy for 2's. Add in a rogue who need only contribute smoke bomb, sap and blind to the mix and you have a very strong comp. The mage is providing the majority of the burst damage here.