Blair was a decent PM until Iraq. I didn't agree with lots of what he did even before that, but he was competent. Likewise (and to prove I'm not being party political) Thatcher, despite the fact I hated what she and her government of vicious b@st@rds stood for and the things they did - hateful but competent. Major, by contrast, was pitiful and largely incompetent. He probably gets away with not being regarded more badly because he did have a hand in addressing NI. For now.
The last 3 have been unconscionably appalling in every regard though. They have resulted in our country becoming a laughing stock on the international stage, as well as helping to wreck it from the inside. History will be very, very unkind to all of them. Which is cold comfort now.