The way the game is set up it seems pretty pointless to use a dps companion I only ever use Healers and I guess if I ever rolled a healer I might use a Tank. So what is the hype with the HK-51? Seems to me its just gonna be another useless companion collecting dust unless they made the game more like Kotor and you could have 2 companions.
You don't need a tank nor a healer for any of the single content. I only use DPS companions. And I spec as DPS too, when I play solo. Kill them and kill them fast: they can't kill you when they're dead!