So many variables....
Last year after watching a Bills game in which Kelly Holcomb was the QB, I turned to a Colts game. Immediately I noticed how few defensive players were playing "in the box" against the Colt's offense. There stood Manning in the shotgun with 4 defensive lineman in rush mode and the balance of the defense back pedaling to cover Harrison and the rest of the receivers in the pattern. This didn't go on for 1 play, but for he game overall. In contrast, the Bill's offense appeared to be blocking the entire defense on many plays last year. They could not run or pass. The Bill's opponents simply showed no respect for the Bill's offense. On the other page was Manning standing in the pocket looking downfield without a strong pass rush or handing the ball off to the RB who found some daylight often.
I'd say you need a good line and good potential passing and running game. No chicken or egg, but decent capability in all 3 areas.
The Bills won't score big until Losman proves he can throw deep. Teams early in the season will likely plan to defend run first and dare the kid to beat them. If he can do that, Willis can get some open space which he needs to get yards. He has not shown that he is a good between the tackles runner yet. Then the Bills can win some games.