zerkers have their place they just can't tank like guardians can and lacking snap aggro is an issue with the class.
alot of the time i either don't have a dirge or a warden but here's just some random clips from SoH on trash, first named and sisters(removed P'Tasa for obvious reasons)as we were lacking the raid to finish the zone that night. i could have pulled alot more mobs and raised my parse about another 1k or so(about 30% of the pulls were simple singles but the patrons of hate were popping 3 adds a bit which inflate zerkers parses).
now taking a parse from an equally fitted zerk vs guardian on a zonewide in VP you will see it leaning more towards a guardian with mythical. zerks are fine offtanks, better than guardians IMO but everyone has their preference. the higher the con the less we parse, guardians deal with this better due to self buffs. why don't i put up a parse of trash in VP? 'cause i'm generally not proud of how i parse after the first floor, now if almost every piece of gear i had would have +slashing then it would be different.
this is all wearing less than great gear but having the zerk mythical does do its job against multiples quite well solidifying our OT role.