Of course, if you want to strip Johnson as a person out of it, that's fair enough. I don't want to pretend that my comments aren't shaped, at least to some extent, by my opinion of him and all he stands for. But presumably there must be some objective criteria to evaluate any PM's performance. What are those?
Take the pandemic response in South Korea, for example. There is a country with a population that is similar to the UK's, and a population density that is even greater. Both of those mean that the pandemic ought, superficially, to have been a far greater threat there than here. This hasn't happened. Moreover, this hasn't happened without even significantly impacting their economy. Official projections suggest that South Korea is looking at a 2% GDP contraction this year, as compared to a 10% contraction in the UK; just to put this into context, the same projections imply that Germany, France, Spain, Italy, the US, India, Canada, Russia, Brazil, Mexico... are expecting contractions of between 4% and 12%, so South Korea is a clear outlier here.*
So the UK's approach has failed economically, and the UK's approach has failed in terms of death toll: we have recorded around 100 times more deaths from Covid than South Korea, and about 70 times more per capita. Remember, too, that the Covid outbreak reached South Korea, and flared up there, weeks before it did in the UK. And then it was crushed; despite two flare-up waves since, on both occasions the disease has been quickly brought under control.
There are at least some historical reasons why South Korea's response was more effective. Very recently, an outbreak of MERS, a more deadly but less infectious disease, struck there in 2015, but that "only" killed 36 people from a total of 200 known to have been infected. Apparently this was enough to spur the Korean Government to develop a programme for rapid expansion of testing facilities if ever there was a need for it. But there's no reason for this lesson to have only been learned there.
In short, then, I'd suggest that the objectively best response in the world to Covid-19 occurred in South Korea.
*Source:
https://www.imf.org/en/Publications/WEO/Issues/2020/09/30/world-economic-outlook-october-2020 ; only China is projected to record any economic growth this year.