no, more subtle than that. they think that economicly, Corbin has an attractive message - whether its viable or not is entirely another matter, and not really part of this - there are lots of people who's living standards have gone into reverse, lots of middle England who fear for the ability of their children to ever buy their own home, and lots of people (and not just of the Corbyn-ite left) who feel completely ripped off by privatisation and PFI. there are large parts of Tory England that do not believe that saying 'long term economic plan' endlessly means that either you have one, or that its any good for them.
they think however that Corbyn's weakness - in terms of being in tune with the public - on defence, foreign policy, interesting causes abroad, NATO mebership, Trident, immigration etc.. will probably more than counter-act the popularity of his economic message, and they also - from bitter experience - know that divided parties do not win elections.
they think that Corbyn will lose the next election on his own merits, but not being idiots they aren't going to bet the farm on it, so they want a plan 'B' - and plan 'B' is having the Labour party self-distruct over the above issues. Labour will probably implode over those issues anyway as they are big, important issues and opinions on them are dearly held and not easily compromised over, but the tories take the veiw that a little poke might help the timing of that.
they also take the view that having Corbyn fall in the first 18 months or so, and having his energised, social media savvy supporters wander off into the political desert having got their fingers burnt on the fire of parliamentary politics would be no bad thing..