Err, that's what you have a Cabinet for surely?
Unless you want to give me specific examples where you think he should have taken the reins.
There's quite a lot of difference as PM between just outsourcing everything to others' agendas (e.g. letting McSweeney making all the political and policy calls, based on spurious polling) and being a PM who doesn't listen to their cabinet and decides stuff without harnessing the combined aptitudes they have assembled.
Maybe Starmer is just a blank slate who is a manager without vision, who just lets things happen if he think he can manage them downstream – that might actually explain why there have been so many political missteps, as he's not really deeply invested in the important calls.