Maybe everyone agrees with my theory?
No, and yes...
So 100% NO to the idea of extremely heavy object to passes over the top of the den. Object like that will leave many marks all around, mostly in damaged small trees(driving over it) that will be spotted during the search/investigation. And probably object like that will get stuck in the ravine till summer as well.
But 100% YES to the fact that they die in the Den or Ravine due to injuries from snow/den roof collapse. Just few numbers: the den floor was about 3m2 (2m X 1.5m), they found it under 3.5m of snow so if they have 1.5m height inside, it mean the roof was about 2m. Wind packed snow weights about 350-400kg/1m3, so just take the 350kg/1m3.
Calculations: 2m x 1.5m x 2m = 6m3(volume of snow over the heads in the Den). 6m3 x 350kg = 2100kg... over 2tons of snow could fall on them suddenly from the height of 1.5m, I think it is enough to make deadly injuries like broken ribs etc. Even if this roof broken into few pieces before impact on them it will be enough to kill.
After being crushed they die under the snow in Den and was moved by water/snow flow few meters down(as you suggest) or they managed to dig out from under the pieces of snow and just crawled out a bit where they die. I do not really matter.
After studied all picture from ravine, investigation reports and witness statements I believe that conditions in the ravine could cause the dead of this 4 hikers without any help from third person.