Think of it as closer to how the US President is supposed to make appointees
with the
"advice and consent of the Senate" (only with the President paying a
lot more
attention to the advice part).
Is Jimbo supposed to be the President or the Senate in this analogy?
Neither, he's the electoral college.
Hasn't the analogy always been the Queen with her reserve powers?
Yes, and that analogy works a bit better. Jimbo becomes the Queen and ArbCom become the Cabinet (considered as part of the Privy Council), the Cabinet is officially selected by the Queen, but on the advice of the Prime Minister (and, by extension, the governing party, Parliament and the voting public - we skip the first two and have direct representation). In practice, the Queen just does whatever the PM says, but in theory she can appoint whoever she likes. Jimbo invokes his powers a little more often than the Queen, of course.