The more downhill oriented a mountain bike is, the more it resembles a dirtbike — more suspension travel (up to around 220mm, where the suspension starts to work against you and makes the bike too mushy for something that light and human powered) , higher and wider handlebars and more space above the seat (nowadays the seats actually move out of the way and come back when needed, operated by a lever on the handlebars).
I'd say that most honest to god OTB accidents happen on slower, gnarly, downhill stuff, where it's easy for the (still relatively light) mountain bike to get stuck and unable to roll over an obstacle in time (before the rider arrives), or for the obstacle to slap your steering to the side, which again suddenly stops the bike.
Dirtbikes are much heavier compared to bikes and the weight of the rider, and you generally ride them a bit faster and not necessarily downhill.
I'd say that most honest to god OTB accidents happen on slower, gnarly, downhill stuff, where it's easy for the (still relatively light) mountain bike to get stuck and unable to roll over an obstacle in time (before the rider arrives), or for the obstacle to slap your steering to the side, which again suddenly stops the bike.
Dirtbikes are much heavier compared to bikes and the weight of the rider, and you generally ride them a bit faster and not necessarily downhill.