Necro is pretty good in PvP. Warlocks are much more rare and are very powerful at high level. Ask yourself, do you wanna nuke or watch a pet beat on people. Necro usually just use pet for transfer pain and nuke the hell out of people. Warlock is a true summoner.
if your priority is pvp there's no question Necro is the best choice.It's the most overpowered class,spend 2 min to check their skills and you'll understand why.
The only disadvantage i can think off is that there are tooooooo many necros for the above mentioned obvious reasons
necros are slightly nerfed in some cases compared to other nukers
the second all 70+ mobs are weak to dark attack ill beleve ncsoft is owned by rl necros