If you look closely at the Mansi, they are fairly small wirey people. I don't believe they could inflict those injuries on the hikers, but it is something to think about, especially if the Mansi were stoned with magic mushrooms. There is still the climbing of the cedar tree, for what reason?
Yeah, if you look at the autopsy files, one of the hikers had 10 broken ribs, with 5 of them broken twice, so 15 rib fractures. That's a shattered chest. By a single blow, since all the fractures are lined. No human is that strong, probably not even a gorilla.
However! In your scenario, they could've fallen while fleeing or been forced/pushed into the ravine.
However!! In your scenario, why was the tent slashed from the inside? Why were the Mansi out at night in the middle of a snowstorm?
But my biggest objection to the Mansi murder theory is that they were an otherwise peaceful people? They jumped straight from peaceful to brutally murdering nine people, then back to peaceful? If the Mansi were violent, there would be records of fights, assaults, robberies, rapes, etc. You don't jump from nice to murdering nine people for little reason then back to nice again.