It's funny: you can already do this kind of move in MH4 and MHG, but the extra animations they added to each step (climbing, jump attack and mounting) does make it look like it's never been done before. I think the decision to make monsters mountable without having to ground them first was a wise choice.
With the added frames of animation (that nice kick-off), the transition looks janky as fuck and is poorly animated (the player is basically glued to the monster's back as it reels and he's on his back) as the camera swings wildly out of control. Also he looks like he's gliding while running. There seems to be no actual friction between the player model and the terrain/tree, they are wallpapered floor tiles.
In general, the player model doesn't seem to have any physics interaction with whats around/under him. Like at all unless its something else physically animated to display the model hitbox.