Those running animations were dreadful
Almost like hes got a stick up his arse or is seriously clenching cos he needs to shit
I don't see a problem there. At least the body armor does not twist around with movement as if it was a part of the guy's body (pointing at you Warband!). I suppose the stick-in-arse appearance is somewhat expected when you have a rigid shell surrounding your body.
The only missing thing is that the character needs to slant a little bit forward while running just to give it a more natural feel. As the commentator says, it is probably going to be fixed. That video is obviously just a little showcase.