Which makes a better ambassador, a political appointee or career diplomat? has an answer from the late John Burgess—but not, I must say, a very informative answer.
The answer, I would have to assume, is no. The ambassador may well be a political appointee, and therefore likely a figurehead. Maybe less so for Australian political appointees, who tend to be ex-politicians, than for the US, who tend to be donors. Politics is at least somewhat relevant experience.
That does not imply that the rest of the staff in the embassy are decorative, and that all decisions are taken centrally in the State Department/Foreign Ministry.