Yea. Lambo had to kill the libs that wouldve eviscerated his ground army. If he sent the corruptors alone to kill the libs which were on top of thors, the thors wouldve deleted the corruptors. So he had no choice but to send the BLs along with the corruptors to keep thors busy while corruptors could attack libs without taking thor fire.
It does not take many Banelings to destroy a Hellbat line. Their splash radius is huge, which is why they not only kill the Hellbats, but also hit the Thors behind the Hellbats that you claim to be buffering.
Without the Hellbats you will lose the Thors.