I hit Greg two times with a winters guile times five melee and it did 1 1/3 bar of his health while not really bad I take you to hunter.
Base combination blow two melees does one bar of Gregs health haven't tested with liars handshake yet.
Now combination blow lasts 20 seconds and is a tree perk not an exotic warlords sigil lasts 4 seconds does more damage yes but is also an exotic and only heals with devour tree.
Here's what i think needs changed it needs a 6-16 percent damage buff and a duration buff of 10-15 seconds.
PS combination blow is an overall better perk because you only need the tree and it only needs 3 kills and you'll mostly use it on orange bars with liars handshake and one two punch it can melt bosses. (see that guy that soloed riven with only liars handshake combination blow one two punch and tractor cannon) And if you don't use liars you have an exotic slot.
Got to say that both the buff duration and the effect are horrible. Even if the buff was just on a melee hit, it would still be bad for PvP. I still would not use it if the buff was 20 seconds. I have only one reason to use the version of the exotic I just got. It has two fusion rifle perks on it. And even that reason goes away in armour 2.0.