If I understand correctly, the chance of a troll spawning after 10 tiles dug using a snake tunnel, would be the same as 10 tiles dug in a straight line, and just as fast?
The vault itself was protected by straight mined lines going north/south/east/west to prevent people from placing a minehole any where near it. I'm fairly sure these were done by Badich, but you fully accepted them by having your villager live inside this vault protected by this exploit. = Winterfell used straight mining bot to protect their vault.
To be clear the lines in the picture below were the ones protruding from your members vault.