Feral bees swarm more frequent as no beekeeper removes thier queen cells. They also move more frequent as their hives are easily destroy by wind, heavy rain, bird, broken branch etc. So once they move, they leave combs that already infested by varroa. This reduces the varroa population in the colony started with new home.
Removing queen cells does not prevent swarming.
Varroa are more commonly carried by drones which can freely move between hives.
When a varroa enters a hive it is looking for open cells preferably drone cells as they are larger and take longer to cap. They then set up shop in the new hive. While drones are prefered. Worker cells will work. The difference with feral hives is that they are capped in a much shorter period of time. Thus preventing the Varroa from overwhelming the hive.
Standard practices in beekeeping meant for a larger cell size for workers. This takes longer to cap. And gives the Varroa more time to establish itself in the hive. If the Varroa is able to find itself with a abundant food source it breeds more frequently. Until such time as it has overwhelmed it's food source and then destroyed the hive.
While feral hives are subject to the mother nature issues you mentioned. I am not sure as to how much of a factor they are in preventing the spread of Varroa. There are plenty of well established hives in the wild that have been in place for years and yet are not overwhelmed by Varroa.
Sincerely,
Brendhan