I'd argue that Rivers is effective within the scope of a given play. BUT, we've already seen tonight how running a wide zone or stretch running game is hampered by the weakside DE having ZERO containment responsibility, so he can just crash down inside all day long (Clowney happens to be gifted in this way). And we know that Rivers is a relic with his poor movement in general (see also: sack at end of 1st half). He's just limited, physically.