I find daily mobs die much faster as Assassination. Just open, Mut once, Env, and then Dispatch. I also throw in a low-CP Rupture near the end to get energy back. Combat can't kill things in a few globals consistently. Chain pulling, multidotting, and AoEing is better as Assassination too. If there's an elite I have to burst down, I just blow Vendetta and SB and it dies extremely fast. Combat has to blow CDs on regular things and constantly utilize BF to stay competitive.
It could just be a gear thing combined with Mut's inherently better opening burst and execute though. If it takes you awhile to kill mobs and you actually get to use a decent amount of finishers, Combat could pull ahead. If you can get the mob into execute range with 3 globals, then finish it another 1-2, I don't see how Combat could be better.