First, that most of that decline is relative power rather than absolute: the UK is no longer astride the world, but because so many others have gained power to kick my parents and grandparents' generations out of their countries, not (in all cases) because the UK became objectively weaker.
Second, that the politicians who caused the decline were doing a lot of smaller mistakes over a longer period.
Those other politicians probably were indeed as you say below average, but Johnson and Truss weren't just scraping the bottom of the barrel, they were the wood of the barrel itself and the floor underneath it.
First, that most of that decline is relative power rather than absolute: the UK is no longer astride the world, but because so many others have gained power to kick my parents and grandparents' generations out of their countries, not (in all cases) because the UK became objectively weaker.
Second, that the politicians who caused the decline were doing a lot of smaller mistakes over a longer period.
Those other politicians probably were indeed as you say below average, but Johnson and Truss weren't just scraping the bottom of the barrel, they were the wood of the barrel itself and the floor underneath it.