I think that Cameron was only marginally better than Johnson.
Under his watch there was a programme of excessive austerity (yes cuts were needed, but not to that extent and he admitted that they would have gone even further had it not been for the Lib Dems), child poverty and the number of people using food banks sky-rocketed, divisions by social class, region or country increase considerably (which he helped drive, through his party's English nationalist, anti-Scottish 2015 general election campaign, joining in with Zac Goldsmith's Islamophobic 2016 London mayoral bid etc.), and his foreign policy record was a disaster. Plus of course he is massively responsible for catastrophically stupid act of self-harm that was Brexit. That excessive austerity and those increased divisions under his watch contributed heavily to the leave vote, quite a few people clearing voted to leave to give him (and Osborne a kicking) so making him front and centre of the remain campaign was a huge mistake, he made a ridiculous and simply undeliverable promises to drastically cut net migration which turned out to be an open goal for the leave campaign, he had repeatedly criticised and blamed the EU for the previous 6 years as PM including for blunders by him and his government, he ran a terrible and overly negative campaign, he arrogantly and wrongly through that he was unbeatable and a genius in electoral contests etc.
The best achievements during the coalition years, legalising same sex marriage, scrapping the compulsory retirement age, increasing the personal allowance etc., were driven by the Lib Dems. The pupil premium policy which divided opinion, but which the Tories and Gove in-particular tried to take credit for, was also driven by the Lib Dems.
