Sunak’s most significant political legacy is that he has brought a form of climate denial politics firmly into the mainstream of British politics, to the point that “a bland statement about a ‘cost’ both parties are committed to” is being written up like this in the Times.
It’s the only thing where Sunak has successfully advanced his form of politics, unfortunately. Stuff that his government is nominally committed to, that was central to the manifesto they fought in 2019, being written up in the Times as if it is a new, alien idea.
It's the Sunak Cost Fallacy, where you don't do a cost/benefit analysis, just moan about the costs. Admittedly a lot of Sunak’s spending was all cost and no public benefit, like eat out to help out or PPE corruption, but that doesn't generalise to all government spending.
Hundreds of millions of pounds in investment over a two-decade period, reducing the cost of a more disruptive climate change and aging infrastructure? Okay, that sounds like a good deal. We say "if it was like a household budget---" but we do renovate homes.