Thats on live? Where its all suposed to be scaled with higher ilvl gear etc? Okey... I dont think we should worry too mutch even before full gear etc, Sure mutilate is really boring to play with 2 min cds, but if you pref sub, youll make it work.
Id say just start duel alot, even tho it might sound noobish but I think its a good way to practice. And i think dueling other rogues is a good way to improve your reflexes as its way more prediction and fast paced then other duels. + you will maybe get an understanding of what he is doing and why, talk about the duel afterwards etc.
And remember rogues are getting buffed in 5.4
I think Rogues will be doing fine with nerfs to other classes, and the new glyphs seams pretty sweet, played some on PTR, maybe dropping imp garrote and faint glyph aint worth it but felt better and "free" in a way. Al long as warriors not getting too strong, I think rogues will have a good time