The quick disengage on pass rush has nothing to do with the Block Shedding rating. The blocker will still disengage whether the BSH rating is at 50 or 99.
Block Shedding rating determines how often block shed animations are triggered. These animations are obvious when you see them and are not "disengage" but instead "rip and move".
I can take any 90 SPD rusher to rush the edge of the Right Tackle and get 2-3 sacks per game in Madden just off the disengage frequency of the RT on most standard slider settings.
The way I'd approach this question depends on the sliders in use. If Pass Blocking is Low (0-25), then the only attributes that really matter for pass rushing off the edge are SPD, ACC, PUR, TKL. If Pass Blocking is High (50+), then ratings such as STR, PMV, FMV become more important.