Warlocks used to be very good at solo pvp, being very tanky with big self heals.
These days, warlocks are all about supporting their team with UA, while their own damage is rather mediocre unless its a very long engagement. Burst is non-existant. Lock survivability now comes almost exclusively from Demon Armors 30% increase to healing, meaning we need a healbot to complete our survival toolkit.
Yes warlocks do fine in 3v3 and RBGs.
There is a reason, however, that you see maybe one warlock every 2 or 3 BGs, and it isnt because they do well =)