To apprecieate Fran you have to know the conditions he played in, no soft league, receivers were able to be manhandled, no protection for a QB. You also need to know that he played in Minny, before there was a damn dome, he played in sleet, snow and ice a lot, considering the division of Chicago and Green Bay it was no break going on the road in the division. Also Detroit was not such a push over as well and was outside.
So given he played a large portion of his career in the elements and had the success he did you really need to look at the whole situation.