Zerker's PvP and PvE effectiveness seems to revolve around knowing how to use Evasive Smash to minimize lost damage and catch people. If you start a charge and the boss moves out of range, or if you move away to avoid an attack or whatever, you should always prioritize cancelling your charge with evasive smash which will buy you another five seconds (and significant amount of covered ground) to release the attack. It severely mitigates lost damage.

I'm pretty happy with my 60 zerker, but the retardation I face in matchmaking has pretty much left me with the choices of: A.) putting Tera on hold entirely until my slow guildies catch up to 60 B.) quitting the small guild of close friends and joining a more dedicated PvE guild. It's lose-lose, either I get pissed off waiting, or my friends get pissed off because I bail on them (had the exact same issue with vanilla WoW back in the day, fuck does it frustrate me.)

But back on topic, the long and short of it is that a good zerker is not a liability in any existing PvE content, but you're going to want to find a good group of people to play with and not expose yourself to the generally ignorant matchmaking crowd (if you value your time and sanity.)