Vidal has always been more dynamic offensively, but he's also just about the most destructive midfield force in my opinion. Matic was comparable in that aspect when he returned to Chelsea initially.
Matic's distribution is quick when he has the ball on his left foot and he isn't pressured-if he's at the base of a midfield 3 then he'll have the space to move the ball relatively quickly. In a midfield 2 where he's pushed further up and exposed to pressing, I think he'd struggle more, and this is what we saw last year. Often he'd have issues circulating the ball because he'd have to shift it away from his right peg to distribute it effectively.
I think Bakayoko and Kante work better as a partnership in a two because in Conte's system as constructed both midfielders have to be able to press high and track back, while as you say Matic is better sitting a bit deeper. Bakayoko is also a very good and underrated dribbler so will bring attacking thrust from the middle as a shuttler, which was lacking last season (at least in theory).