This may be a silly question, but how is Craven planning to get down to the level where Kerwyn is?
Kerwyn and his elevator are at the bottom of the Obelisk.
Although Craven could spend several minutes winching the elevator up from the bottom while standing at the top of the Obelisk, he is not going to be able to avoid standing on the purple veins for a long amount of time if he is winching the elevator up.