for me personally, mt biking is more prone to injury than skiing or boarding. snow is way softer than dirt and rock. not that there arent a lot of ways to die on the snow, but ive been snowboarding for 35 years and mt biking for 32 and ive been hurt way more on the bikes than the boards. it all boils down to how dumb you are vs your brains self preservation level.
mt biking isnt low risk most of the places we ride. weve had friends wreck and end up so far off trail that we didnt see them when we went by. when you reach the bottom of a trail and the guy who was in front of you isnt at the truck, theres a problem. started riding back up and 2 hikers asked if i was missing a friend. i said yes and they told me he was in pretty bad shape (and didnt help him?!). he was knocked out cold. full gear, just caught a rock with his pedal that was hiding in a clump of weeds and it launched him down into a thick gully about 30' down the mtn. lots of blood and he was concussed, but no broke bones.
"understeer is when you hit the wall with the front of your car, oversteer is when you hit the wall with the rear of your car, horsepower is how hard your car hits the wall, and torque is how far your car moves the wall."