I'm not interested in the stats mate because they are rarely useful without context. I can tell how well a player is playing by watching them, and Dier has performed very well and consistently this season. The centre CB is always going to be less involved stat wise when the players in front and either side are performing well. His job is to organise them. If he had to make 5 tackles and interceptions a game I'd be more worried because it would mean thiose around him were leaving him heavily exposed all the time. The CCB is there to organise and make sure everyone else is where they are supposed to be and to mop up if everything else goes to shit. He's done that very well.
I think Dier has done well too and I can see that with my eyes but its an easy role to play. Stats just confirm what Dier is, solid above-average defender. There are better passers, better goalscoring and more athletic defenders out there that could be an upgrade on Dier. As an example If we had Sergio Ramos in the middle of defence, we'd get 5 goals from that position and some very strong leadership.
At the minute from Dier we get good organisation and an above-average passer. It's nice but it can be improved on and make us a better team if like I said we could get goals from that position or someone who is an elite passer.