I played DE thru JV in highschool, then was too small and changed positions for varsity. DE number 1 responsibility, regardless or pass or run play, is to "set the edge". In a word, containment. Nothing gets outside your outside shoulder. Ever. When it does, unless you are double teamed or steamrolled in the earhole by a pulling guard....you are likely getting called to the sideline while somebody else contains for a few plays.
Kongbo was terrible at this. Honestly, it would be different somewhat if he got mucho sacks and lost contain sometimes because he was always right on top of the QB...truth is he almost never got sacks and still lost contain on run plays all the time.
When a RB or scrambling QB gets outside the DE, the cornerback is long gone running with or being blocked by a WR...its nearly always a BIG gain for the offense, and usually puts the RB in a 1 on 1 situation with a safety or OLB... if the RB can make that 1 man miss, or a TE or lineman gets downfield to block....off to the races. Touchdown.
Tl,dr....Kongbos job is containment. He sucked at it last year...hopefully with better coaching and discipline...