Historically, a main strength of the AT ko had been that people were getting 80-95 k miles per set, making them less expensive in the long run. The Duratracs have been - so far, getting closer to ~ 60k, but, are more aggressive. The more aggressive a tread, typically, the lower your mileage on them.
Essentially, the AT ko are aggressive AT's, and the Duratracs are Mild MT's (Called Commercial Traction in tire lingo). The Duratrac is a much more modern design, albeit the sidewalls seem to be prone to rock rips in some terrain, cactus needle flats in the tread, and some other durability issues that the AT ko seems to be better at (But not invulnerable to)
The General and Cooper have their newer AT variations that are very good, if slightly less aggressive than the AT ko and Duratrac.
When you look at tires that will be used of road, and, in snow, for DD's especially....there are typically compromises to be made.
Essentially, the softness of the snow or terrain will dictate what type of tread works on it.
So, if where you drive, the snow is hard packed/icy, an MT or more aggressive tread pattern, as they use large tread blocks that have to sink INTO the surface to get bite for traction...the way a paddle wheel work on a paddle boat...will NOT be able to penetrate the surface unless its soft ENOUGH to let a tread element sink in.
The harder the surface, the smaller the tread elements need to be to still sink in.
Its the same principle that tells you to wear sneakers to play basketball on a hard court surface, and cleats on a wet grass field for soccer, etc.
The cleats can't sink into the basketball court, and you skitter along w/o traction.....and the sneakers would slip/slide like crazy on the wet grass as they have nothing TO sink into it...but grip like crazy on a the concrete.
The deeper the snow, the better an aggressive tread works. The harder packed the snow is, the better a less aggressive tread works. This is one reason you can have 2 people argue that the SAME tire SUCKS, AND, ROCKS in "snow".
If one guy's snow is softer, or harder, what works, and doesn't - will be different.
So, they are both right, but, if going by their recommendation, you want to have the same snow they did for it to work.
If you want a dedicated trail rig, MT's are almost always better, as the large aggressive tread elements work like paddles through the goo, and can wrap rocks and terrain better. For sand, an AT is sometimes a better compromise, as they tend not to bury themselves as easily/have more contact surface for floatation.
For hard dirt, AT's again have an edge, for the same reasons...an MT can't sink large elements into the dirt if the dirt is too hard...but can if the dirt is soft enough.
So, you choose the weapon(s) that make sense for where you go/what you do...and, know that for
other conditions/scenarios, you MIGHT be wearing cleats to the basketball game and sneakers to the soccer game, etc.
The same goes for whether a tire gets rock damage. Rocks are not all the same. Some areas have sharper rocks, and/or rocks that tend to present sharper edges than others, due to the geography/geology of that area. Some trails are wetter, or drier. Wet rubber slices much easier, so, wet sharp rocked rails are much more sidewall deadly in general for example.
That again leads to the same tire sucking and rocking in rocks, depending on what rocks. I always recommend going with whatever the other experienced people in that area go with, as, that's typically what works there.