Not sure about that, the Cowboys receivers were among the league leaders in dropped passes in 2019.
he can teach only so much in regards to technique and how to focus, he cant place stick um on their gloves ...no WR coach can catch the ball for you.
my eye to Sandray is teaching them route techniques, how to dip and sink their hips, footwork, selling the routes ad deception- extent arms
out of the breaks, adjusting and improvising on the move, how was Sandray LaI full body ofwork -did the WRs route and development improve (ala gallup) was it just a matter of McCarthy wanted a change up and his own selected guy ( adam Henry)
I hear he's pretty good because he actually has WR drills.
I heard from past players that sandray was more detailed extremed technician than most wr coaches and placed more emphasis and stress on stance, running form, footwork, waist bend,,dipping the hips, shoulder placement, etc.
I can't imagine a prominent wr coach not knowing schemes as per whispers from the stars so I'm taking that with a grain of salt.