Since overalls come into play when making trades in Dynasty Mode, I'd say that the overall rating needs to correspond to a player's value and reflect their overall abilities, regardless of where their strength lies; in effect, it also kind of ranks the players in the league. Ideally, the calculation would be weighted in a way that allows great players who aren't too athletic or brilliant in many areas but kind of average in a couple of others to still be rated highly, while players who are tremendous athletes but a bit unpolished skill-wise wouldn't have their overalls appear artificially boosted. Great all-around players with the highest production and the truly elite superstars would naturally have the highest overall ratings, representing their status as one of the league's most valuable players.
I too like the idea of impact and role playing a part in determining the overall, and balancing things out when a player does have some deficiencies, but it still one of the league's biggest stars and extremely valuable to his team.