If other teams have a playmaker at WR, they can get him the ball by moving him around and it's harder for our defense to adjust to. Sometimes we'll run a cover two and there is a period where the guy is behind the CB and the safety ain't there yet. Sometimes we'll play way off the guy (actually we do that often) and it opens up quick passes. That's just how our defense is built. I think with Fant the other teams are basically doubling him with a LB and a safety and one of them is told "don't bite on the run at all, just stay with Fant" which takes away the chance for the play action.
The fact is, they can do that on our offense because we don't have the playmakers on the outside to punish them for allocating safety help to Fant every play. We don't have the RBs to punish them for not respecting the run when they try to double Fant and make sure one guy doesn't bite on a play action. When you lack playmakers at WR and RB and can't punish the defense for a double team, you're in big trouble and it goes beyond X's and O's. Furthermore, the line ain't great, so even if we had a guy on the outside who could torch the defense deep, the QB ain't got time to throw, and even if he did, he probably would airmail it 3/4ths of the time. And because the line ain't great, there's almost always an unimpeded defender waiting for our RB either at the LOS or within a yard of it, so it's hard as hell to run the ball for even 3 yards in such a scenario.