True, the robot doesn't have an in-universe reason to exist (that we know of), but its existence reminds us this game is not meant to be taken too seriously. Power Vacuum is largely a parody of the "house game" genre, poking fun at the common tropes, so similar character archetypes or situations are deliberately ironic.
I strongly disagree about Hunter, he's the catalyst for the whole story. As the villain, he's proactive when Sterling is mostly reactive. Hunter creates the conditions for Sterling to get the girls, through the use of drugs and hormones that raise everyone's libidos while lowering their inhibitions. Hunter's also responsible for Sterling's physical transformation, through the use of Human Growth Hormone, although Catherine's training was necessary as well.