I agree with this sentiment, compared to the average DPS across all of the different specs Demo and Destro are fairly strong. It is only when you compare their damage to some of the arcane or affliction parses where they start looking underpowered.
The only thing that I would ask for as a Demo warlock right now is for them to stop making fights with damage increase mechanics that don't effect pets.....and for them to give Demo some sort of fury return that works like Shadowburns; any add that dies within Xs of hitting it with Soulfire gives X fury instead of having to get the killing blow. It is one of the mechanics where I feel Demo can fall a little short; fights where Afflic and Destro can gain near unlimited resources but Demo is stuck with the base amount.