Not sure that is a sleeper. Dallas needs playmakers on defense. He checks that box. 54 and 55 are complete zeros. He and Surtain are logical first picks if defense is it.
He is the top ranked LB in this draft, that's not asleep.
Top-rated \ best defensive prospect for this draft is Micah Parsons.
Viewed close to 30 mock drafts to date; 1st defensive player picked-predicted off the board has been overwhelmingly Parsons. The highest I've seen is him going @ 7 to Detriot; most of the selections are the LB going to Denver with the 9th pick.
Only four times did I view another defensive player going before him - CB Farley @ 4 to Atlanta (by a Falcons homer blogger), LB Jeremiah Owusu-Koramoah @ 9 to Denver, and CB Surtain twice - again to the Broncos.
If the Cowboys select Parsons as the no. 10 pick as Redball Express predicts - that will be a surprise...and shocking.
99% chance that Parsons, or one of the top three corners (Farley, Horn, Surtain) will be the first defensive player selected in the 2021 draft.
In summary- Micah Parsons is not a sleeper .