It's a fairly simple pattern. Both of the pivots need to be good passers and, more importantly, good at reading the development of the game and the move. They need to be able to control the game with the ball/with movement as well as chasing down the opposition and taking it from them.
Winks and Dier are both pretty good positionally and are both good on the ball. Winks might not tackle as well as Sissoko and Dier might not run as fast, but for our kind of football that's not really required. If we still had a fit Dembele we'd have a very difficult choice for two of three midfielders, but without him it's a very, very easy selection.