Saints offense was 9th in total yardage and 3rd in scoring, in a year where we played 5-3/4 games with a back up QB and most of the season with our star RB hobbled by a leg injury, and by all accounts.... no viable weapon at #2 WR.
So the knock on SP is likely very situational. In the long run, his offense is borderline elite. You can break it down to some specific situations where it didn't work so well, but I think you'll find that is the case with every football team, past, present, and future.