What would be a politician's ideal outcome of a stint in politics?
I think that Trump and Berlusconi and Cheney and Netanyahu all aim for maximal wealth (and minimal imprisonment) for them and their buddies - and they do very well on this front! So are you sure they are unable to make "good decisions" from that perspective?
On the other hand, I think that people like Macron and Merkel, but also May, Truss and probably even Johnson, are more motivated by their legacy and truly would like to improve the status quo of their country - and they believe that that is their path to greatness.
So I think this sets apart the UK politicians from the "real" grifters. But at the same time I think they are also easily distinguished from people like Macron and Merkel and even Von der Leyen, because the British leaders are just so spectacularly bad at it. Starting at least with Cameron's referendum decision we have witnessed a remarkable sequence of massive unforced errors by UK politicians, the likes of which I have not seen in other "Western" countries or the EU (despite your insistence to the contrary).
Maybe "terrible governing by people who nevertheless care" captures it well.
So I guess where you see "evil" I see "haplessness" as a defining factor among UK leaders. A competence gap was my way to explain its origins.