Magahee and Williams are top-tier WR's. Nance is a top-tier RB. And, in the only game I saw first-hand (OSU), the o-line gave him more than enough time... His supporting cast isn't as bad as so many want to believe...
McGaha is a premier POSSESSION receiver. He'll be a fine third- or fourth-option for someone in the NFL, a chain mover in the slot. How many catches did he have against OSU? 15 for 165? Sullivan's finding him and getting the ball to him.
That's part of the problem.
Williams wasn't playing from the LOS last week because of a hamstring. The rest of the receivers are almost lost causes. Take Gerrell Robinson for example, who has four dropped passes that hit him between the numbers. This is a guy who can do real damage in YAC but he has hands of stone. Or Kerry Taylor, who should be putting up six or seven catches a game, but is suddenly spending more time freelancing on his routes (part of it because ASU's short passing game just doesn't stretch the coverage to get him open).
Nance is NOT a top-tier RB. He's a second-stringer on a good offense, the change of pace guy you bring in for the every-down back. Nance has no big-play ability whatsoever. This is as far as his career goes. The guy who does have every-down big-play ability -- DeWitty -- has been MIA. I can only assume he's continued his poor practice habits.
All that said, I do agree with you the parts don't add up to what we're seeing. They should be better, and Sullivan is *part* of that problem. But the bigger problem is who is running the offense. I suspect Erickson has bit off more than he can chew and there's a dearth of coaching for the QBs. We saw this the past two years as Carpenter continued to disintegrate and no effort was made to move the other QBs forward on the depth chart. Reality is none of them are improving, and I think the coaches went into this season thinking they could improve just by eliminating sacks and interceptions. They're more or less doing that. They've also stripped the big play potential from the offense. Defenses have no fear of ASU going downfield, and that's all on the coaches, not the QB, not the receivers, and not the OL. They stick to the shotgun which limits a vertical passing game and gives the defense a one-up on the running game.
You can bash Sullivan all you want -- and some of it would be fair -- but realize Sullivan is doing EXACTLY what the coaches want him to do. That's why he's still in there and why Brock isn't. They don't want Sullivan to challenge the defense by throwing into coverage, which is what you need to do four or five times a game to make a play. In the NFL they call it "throwing a receiver open." Warner has made a career out of it. Of course, Warner could hit a gnat on the run 30 yards down field and Sullivan can't, but the coaches have made little effort to express confidence in ANY of the QBs to give it a shot. They just don't have any expectations of the QB at all. You will never get great play from your QB under those conditions.