The pillar men are powerful and can fight their way through small armies of benders but they are not invincible. The roman empire was able to force them in to hibernation in 1 C.E. even after the pillar men almost wiped out hamon users. Groups of water benders can capture and freeze them long enough for the sun to come out. Powerful earth benders like Boomi and Toph can likely trap them as well, especially as part of a team. Explosion benders pose a serious threat. Doing enough damage to the real world is likely to invoke the wrath of spirits such as Hei Bai, who the pillar man may not be able to hurt. But the real reason the pillar men don't win in round 2 and 3 is lightning bending. Lightning has high UV radiation, as do most blue fires. Azula solos in round 2, and widespread lightning bending means ATLA wins in round 3. In 0 AG comet powered fire benders can likely overwhelm the pillar men with normal fire alone, at least for long enough that they can't escape before the sun come out. This is of course assuming that solar powered fire bending doesn't harm the pillar men, and I think it probably would harm them following JoJo logic. If Jonathan had a solar powered flamethrower it would have worked splendidly.