Game play aside. Capping energy aside. Missed GCDs aside. It all comes down to numbers. Every simcraft type thing out there will tell you that combat currently sims higher than any other spec especially with the T15 4 pc. bonus. Math doesn't lie. If 1 + 1 = 2 then combat should have some insane parses out there but it doesn't. Especially now after so many people have gotten used to playing with the 4 pc. bonus and are used to all the boss mechanics it should be almost reflex by now for some people. There's also a reason that so many fire mages are popping up around WoL because of RNG and random mages are getting the blessing of RNJesus and pulling insane numbers. So with all the geared combat rogues out there. All the random RNG that gives some combat kid a perfect fight.
Let me ask you this my friends: Why hasn't some insane Asian kid out there with like 600 APM and an awesome internet connection with 0 latency pulled higher numbers than assassination? Why is it that on every fight assassination simply out performs combat time and time again? Why is it that even though the math says it should be so and that there has been enough fights for RNG to proc some perfect fights for combat that combat is no where to be seen on the logs?
The class is just under tuned. Even with a perfect game play assassination still pulls higher numbers. Combat needs more than just simple tweaks here and there. It needs pretty big buffs. Even if everything stays the same the fact of the matter is that combat needs to have its damage raised up. While QoL issues would be nice to be addressed combat needs a straight buff to bring it in line with assassination.