He's only in Parliament in the first place because he wanted to be Ed Miliband's Attorney General. He doesn't like Parliament and barely knows his own MPs. He's never spent any significant time as a backbencher. He was promoted to the front bench because people were dazzled by his legal credentials. He was picked as a figurehead by the McSweeney operation precisely because he was basically apolitical and had no strong ideas of his own. And he won the leadership, partly because Labour members won't vote for a woman, and partly because neither Nandy nor Long-Bailey caught the imagination.
The trouble is that, once you're PM, you can't be a figurehead. There's a lot of boring bureaucratic stuff that you personally are responsible for.
I've said before, Boris was a fairly good mayor and a terrible PM. He could carry it off as mayor because he had a capable team doing the boring stuff, while he spent his time on the high-energy bumbling salesmanship that he's good at. He couldn't do that as PM, and ended up the tool of his officials.
Sunak didn't have the aversion to boring work, and was very assiduous at doing his boxes, but he didn't seem to have a vision, and nobody knew why he wanted to be PM (except to impress his FIL). So Whitehall was directionless, just in a different way.
Starmer is very like Sunak in that sense. He seems to hate the job, nobody thinks he's any good at doing it, and sometimes I think the only thing motivating him is the desire to have his own way, which is why he sticks with bad policies long after he should have dumped them.
There's a book on the history of the Ottoman Empire that explains the decline of the Empire just by them being unlucky enough to have 13 bad sultans in a row. I'm struggling to think who the last good PM was - not in terms of agreeing with them, but in terms of their ability to steer the government and get things done. Maybe Blair's first term, and that seems a lifetime ago.