Thats just not true. RF has been playing legitimately great this season, and not just by Bills standards. We're talking league wide, he has better numbers than anyone besides P. Manning. You insert anyone else in there and all the chemistry is gone, all the receivers might suck again, the line might suck again, etc etc.
It might be a good idea to take Luck as a 'best available,' very long term type of pick, similar to Spiller last year. You don't get a chance to draft these kinds of guys every year. But lets be realistic, RF has this job for as long as he keeps this up.