Base it on the league/timeframe.
Each league is different. Scoring, number of players/coaches etc.. Even timing. If you want an overall rank fine but how about ranks in your league. I have a league from near the 2000 that ended after 2-years and the new league with different rules for the last 15. The leagues were nothing alike, you should be able to split rankings based on the league/time-frame in addition to an overall score.