The point about policy is that you have to prepare the way for it. It's no good pulling it out of nowhere at the last minute, and expecting people to lap it up (arguably, Labour made this mistake with some of their policies in 2019). For example, it will take years to shift public attitudes towards immigration, given where we are now, so best make a start because, you can be sure the far-right will weaponise the issue in 2024.
Maybe Labour could learn a thing or two from Merkel, who remains popular, despite welcoming immigrants into the country five years ago:
https://www.theguardian.com/world/2020/aug/30/angela-merkel-great-migrant-gamble-paid-off
Come to think of it, Starmer's "boring but competent" approach could easily be modelled on Merkel's. I wonder if it will pay similar political dividends in the long run.
I'm old fashioned, and remain stubbornly attached to good and necessary policies rather than chimerical notions of "electability" and "leadership". If Starmer runs on a 2017 style manifesto, I'll be delighted to vote Labour and over the moon if they form a government. If Labour tacks hard to the right to win back socially conservative voters, I expect I'll still vote for them, but don't expect me to be popping the champagne.
This isn't a matter of "ideological purity", it's about the long-term prospects for the UK, as opposed to the immediate challenge of winning in 2024. Fundamental changes are needed to address the historic challenges of climate change, automation and a growing elderly population. The 2017 and 2019 Labour manifestos were pretty good blueprints of what's needed. Without those changes, I see the UK sliding inexorably to the far-right. If Starmer is elected in 2024 and merely "goes with the flow", it will at best be a temporary brake on the unravelling of social democracy in the UK - just as, for all Tony Bair's thumping majority, we now live in a world where the political agenda is set by fascists like Nigel Farage.
Of course, I'll breathe a sigh of relief if Labour win in 2024. But if Starmer squanders the opportunity to make big changes, it will be short-lived.