Slayer and Choppa are good at shutting down BW/Sorcs (any dps really) because of 100% crit chance reduction debuff and -50% parry/block debuff is no joke.
Mara and WL don't come with any 50% healdebuff and their singeltarget is mediocre in aoe spec even though they will have access to an execute ability.
Mara and WL will spend majority of their time using aoe abilitys whereas Slayer and choppa will go between singeltarget and aoe.
Thus not making it hard to understand that they will fall behind in the damage meters.
Slayer and Choppa is not a newbie friendly class to play.
If you dont manage your rage you will not melt, you will explode.
A sec need to find my totally none biased screenshot.. hang on.. ah found it.

( yea I know not the same caliber of wb fight as the previous poster, 1-2party premade with random people on both sides I think.)
Here is a pic of a good/experienced Choppa player vs the 2 bottom ones, the diffrence is HUGE.
It comes down to the skill of the player, also rr, gear, proper stats stacking.
Teamplay is 100% key in this game and for the love of god stop looking at things from a microscope point of view.