Given all these questions it tells me very little about what ethical system is being discussed when someone uses the word 'utilitarian'.

It does substantially reduce the decision space. For example, it is generally a safe-bet that the individual is not going to subscribe to deontological claims that say "killing humans is always bad." I'd thus be very surprised to ever meet a pacifist utilitarian.

It probably is fair to say that given the space of ethical systems generally discussed on LW, talking about utilitarianism doesn't narrow the field down much from that space.