Drivel. You want to ignore Johnson because it doesn't help your 'argument'. Having 'experienced' people by your argument, gave us a serial incompetent liar.
Nope I actually haven't ignored Johnson, but when you are considering a trend that goes back 170 unbroken, trying to make a point about a single PM rather than the totality of PMs since 1852 is missing the point.
The point remains that for the past 170 years every PM has had the experience of one of the great offices of state or been leader of the opposition. In many cases more than one of these experiences. That is a simple statement of fact and the reason behind this is because it has always been considered that this level of experience is important.
I suspect this 170 year trend is about to be broken, perhaps as early as next week, when we end up with a PM whose greatest level of experience up to that point will be two months as Defence Secretary. Perhaps she'll be great, perhaps she'll be awful - but you've already alluded to one of the issues - we have no idea about her because she's never had any significant scrutiny on her which would have been the case had she held one of the great offices of state or been leader of the opposition.