The warlock will not pull his/her own weight initially.
But with the CotE, the others will each improve by a large margin (3 DPS improving by 13% each = 39%).
And you'll probably be close to what you were before (lock only has to do ~60% of any one shammy).

And then down the road, as your lock gears up.
He should get fairly comparable to your shammies.
And then you are golden.