He has been an average player the last couple years and was 4th on the 2018 white sox in fWAR. A 2 WAR player is an average starter and Yolmer has been that the last couple years.
This statement does not excuse his play this year at all, his play this year has been ridiculously bad. It's not just a slow start - guys get off to a slow start with the bat sometimes even if they're doing everything right, but his defensive mental miscues make this something far worse. Either mentally or physically or both, he's not there at all right now.
This is particularly disappointing, because if he was just doing the same thing as last year, there would already be teams calling about him. All he had to do was be a fundamentally sound, average infielder who can play several positions. The Yankees could use another of those right now. But of course, somehow, lack of preparation or poor coaching or poor focus - always has to screw over our franchise.