Lightning rods definitely do (and always have) fully protect everything in a certain radius around them, since the game only checks for a lightning rod after choosing the final location to strike. A single cobble pillar is still not sufficient, this has been noted on github https://github.com/BTW-C...

If I've understood the current mechanics correctly, the lightning rod doesn't fully protect any surrounding area except in combination with other lightning rods or blocks although it can significantly reduce the chance of a building to be hit, it doesn't on it's own eliminate the possibility within ...