Oddly enough, I had the most success with the smallest forces. Usually just my companions. I immediately have them all retreat. With a fast horse, three large quivers of obsidian arrows and a bow I can take out 100+ at a time than retreat. Than repeat until you wipe out a group. So long as the horse doesn't get injured it works. It is a pain, but it works. Even managed to kill the Night King a couple of times Unfortunately, it only takes a couple of mistakes and you die. So successfully completing this strategy enough times to defeat all the white walker armies is unlikely. And not really very enjoyable. Tons of XP though each time you do defeat one of their armies.

You are right. I have tried with a large force of nearly 200 of my own troops, a dozen or more companions, even joined up with John Snow leading a force of 400+ Nights Watch. Our forces were slaughtered. Did not matter how many of my troops had obsidian weapons or fire arrows.

Tried with a force almost exclusive of cavalry armed with fire or obsidian arrows, thinking they can fire arrows and stay at a distance, but did not work.

Started maybe 12 to 15 games. Of the six or so I was still playing when the White Walkers invade, i quit all of them during the War for Dawn, even the ones where I was able to destroy two or three of the white walker armies.