Again if you read my posts I've said several times that having a lot of defensive actions doesnt automatically mean someone is a better defender.
Mustafi makes a lot, but he also makes lots of mistakes. He's a hard worker prone to cockups and making cockups isnt good for a CB. Phil Jones is another one, when he has a decent game (and its more likely against mid table or lower teams) he tends to make a good number of defensive actions and also plays a lot of decent passes etc. So his stats rocket up from those matches, hes a bit of a flat track bully for CBs.
That said Smalling was one of the best CBs that season. Not as good as VVD no, because VVD is also better on the ball. But Smalling at his best is a dependable CB with very good defensive instincts who is pretty good at covering when teammates are out of position.
He wasn't at his best last season - like Lindelof he was more passive with fewer defensive actions than the previous season, not as willing to try and win the ball earlier on in moves. He still made more than Lindelof just not as many as he had done the previous season. At least with Smalling I know that he can put in a hard graft and play with an attitude to win the ball because he's done it in the past, but more importantly he did it only 2 seasons ago. So he's done it recently.
Lindelof is yet to show that he can play with that determination to try and win the ball a good amount. We're into season 3 and so far my opinion is that he isn't going to show it, so I'd like to see if Tuanzabe is going to show more to his game than Lindelof. Because I think we wont have one of the top defensive records this season despite our big CB signing and when that happens, we'll probably sign another player to fix that unless Tuanzabe shows enough to suggest he can do it himself, or Lindelof becomes a more effective defender.