I dont judge a GM solely on players drafted. There is free agency and little gems accumulated during the season. No GM is knocking home runs using just the draft. Players like Cody Ford and Kaiir Elam would have been selected high even if Buffalo passed. Brandon Beane is much better at finding talent after round 3.
Also, some drafted players are not very good as pros, I call them landmines, be careful where you walk.
Overall I give Beane an B+ at acquiring roster talent.