The haplessness is a routine that Brits absolutely love, and again it takes no small skill to be professionally hapless. This was also a staple of Wogan's performances; famously, for the big Children in Need telethons, he never did any of the rehearsals but came on and delivered a charismatic and funny performance - all night.
The problem is that Johnson is not applying for the job of chat show host, he's applying for PM, and this routine absolutely does not work on other EU leaders. He also appears to be entirely self-centered and amoral. Years ago having a daughter in adultery would have disqualified him ( https://www.theguardian.com/politics/2013/may/21/boris-johns... ), but in post-Trump times nobody cares.
http://www.harrowell.org.uk/blog/2017/12/11/the-two-cultures... : explores this concept at greater length. As a Cambridge alumnus I'm absolutely familiar with brilliance as a kind of performance. For those in that culture glib effortlessness is prized. An earlier example might be Enoch Powell's showboating on his Classical Greek paper - when asked to do a translation into Greek of a poem, he did two versions as pastiches of different Greek poets and then left early.