Yes Dick, all PMs have made mistakes but not all have been inept. And please provide the source of your C&Ps. The above is obviously not your own work.

I located a Guardian article which I think provides a good balance of views.

Sub title is "Risk-taker, pragmatist, placater – or all of the above? Six leading historians assess Cameron’s aims, achievements and failures as prime minister"

I don't think it is particulary an appeal to authority as it does give half a dozen different views