Hint: Corbyn had the lowest vote to seat conversion ratio for decades.
That is an effect of the way the constituencies work, it has nothing to do with his abilities or popularity.
Hint: Corbyn has the biggest swing in decades, with a 9.6% increase in proportion of votes gained, and 10.3% in England.
https://en.wikipedia.org/wiki/Results_breakdown_of_the_United_Kingdom_general_election,_2017
The reason the cons are so terrified of Corbyn is that the cliff-edge design of the UK system means that he only needs to score a small additional swing in the next election to achieve a thundering majority, and a lot of the cons will be out of a job.
They are right to be scared. You only have to look at the remaining right-wing media to see they keep up a constant barrage of propaganda attacks to keep their (mostly elderly) supporters on their toes.
Luckily for the cons, there are still plenty of ignorant and ill-educated people around, and tory policies for state education of the poor will maintain the supply. As the FT says, "In short: better-educated people tend to vote for leftwing or centrist causes, while those who never went to university are more likely to vote for rightwing or populist parties."
https://www.ft.com/content/dac3a3b2-4ad7-11e7-919a-1e14ce4af89b