But boring doesn’t automatically mean competent. People’s main criticism of Starmer is that it’s unclear whether he has any actual beliefs or if his core philosophy is “say/do nothing controversial and pray your enemies implode”. How that translates into governing is an open question and there’s a real risk that his lack of an animating philosophy is great as an opposition leader but just leads to gridlock and inter-party bickering when in office from a lack of leadership & direction.
The problem with running on “I’m not the other guy” is that your support can be wide but also shallow. There’s a real risk, as predicted in more than one dystopian British near-future fiction that a right wing government would be replaced by an ineffectual left wing centrist pap that disillusioned people so much to politics that it allowed for the rise of an outsider firebrand populist. I think it’s a serious risk the UK is facing in light of a Starmer leadership.