For the Yankees to surprisingly contend this year, they needed players to put in some surprising performances. That was especially true regarding the pitching staff, as there was plenty of consternation about the rotation's depth all offseason. So far the rotation has performed well, posting a 3.93 ERA as a group to go along with an 8.75 K/9 rate.
In order for that to happen, they needed mercurial pitchers like Luis Severino and Michael Pineda to be the best versions of themselves, as they have. It was also necessary to find someone to fill the vacancy at the back of the rotation, and that is what Jordan Montgomery has done capably.