He plays as a LB,simply because he is the only one who can actually do the job there, he played RB a little bit last season, but there was obviously going to be an adjustment period considering he hasnt played there for the last 3 years.During his first season here...the only one he was actually a RB, he was fantastic and very eager to join the attack,he was actually known as an attacking full back when we signed him but he evolved into a much more balanced player on his time here, and he is actually a very good crosser of the ball,he is quite capable of attacking, but he prioritizes his defensive responsabilities first,which IMO is a very good thing for a FB, all in all, i consider him to be the best FB in the league, and i dont think alot of people will disagree with me.
As for Matic,if you dont think he was close to Busquets during our title winning season,when he was being praised left and right by every single pundit and even fans from opposite teams,then i dont know what to tell you