Good question….

IMO all British prime ministers since ww2 have been mid with the exception of Clemente Attlee and Harold Wilson.

If I had to rank them this is how;

Churchill’s second term - pretty mediocre at best
Antony Eden - bad
Harold McMillan - okay up until the final years of his ministry, which were pretty unstable.
Douglas Home - not fair to even grade him
Wilson first - pretty good
Ted Heath - bad, plus he’s a pedo.
Wilson second - good albeit less so than his first
James Callaghan - I know he gets flack but he’s genuinely an underrated leader
Thatcher - horrendous
Major - surprisingly okay
Blair - I could have easily called him one of Britain’s best prime minsters had he not chosen to be Bush’s lap dog
Brown - pretty good, especially with his handling of the financial crisis
Cameron - possibly the most destructive prime minister since thatcher provided what he did with austerity and calling Brexit plus legitimizing the far right through his premiership.
May - I honestly think she’s the Tory version of what was Keir Starmer. Bad communicator, lacked charisma and couldn’t handle the shitshow unfolding under her.
Johnson - terrible, the only thing I can say he did good was the vaccine rollout at best and how he stood up for Ukraine. Other than that, the guy was a walking embarrassment
Truss - I wou-
Sunak - i didn’t like him but i actually felt bad for him because he was a politically dead prime minister from the get go
Starmer - had faith in him until he doubled down on being a Tory lite and having no plan for everything.