Steve:
I think you're being a little disingenuous (or looking through RED-tinted glasses) in claiming that Corbyn trashed May's majority.
My view would be that that was mainly down to Theresa may failing to make good on Brexit, and making too many concessions to Brussels thus leaving us in a much poorer negotiating position.
If it was down to Corbyn, why did he not repeat the result against Boris two years later?