Yeah... No toughness ranking will ever be perfect. Toughness is a subjective concept that depends on match-ups, rosters, gamesmanship and a hundred other things that aren't quantifiable.
And if I tried to accomodate situations like IV.49's by including data like effort and enth, calculations would be prohibitively complex and (I think) even more subjective. After posting my rankings I considered that you could use something like average BBStats for al games in a league (from the USA NT offsite scouting tool). But I'm not willing to spend the time collecting and collating all that data. And I don't have the computer know-how to create a tool that would do it for me.
You might cite even more evidence that these rankings are a bit off: Prairie Dogs
(29602) has the top NR of any D.IV team (owing to his long cup run this year). But in the two rankings, V.41 (his league) is ranked 5th and 9th. Surely they ought to be considered for toughest league overall.
Maybe I should have shown the ratings as ranges. And if I hadn't slept through my college math classes, I might have known enough about statistics to put a meaningful range on the ratings. In any case, I wouldn't take them too seriously. Like I said, this exercise was mostly to spend time on my day off and is (insert sarcasm here) *very scientific* ;-). If you're near the top, you're probably about as tough as any other league near the top, regardless of exact rating.
In defense of my rankings, however, I would say that knowing when to CT and when to TIE are part of what make teams tough. Practically, published team rankings and game results are all we really have to go on. Who wins and loses and point differential are what put you in place to promote and demote. And IMHO that's what matters, because toughness is all about how hard it is to promote and keep from demoting. If you've got a weak team with HCA throughout the playoffs, it's easier to promote than if a strong team has HCA. And a measure of league toughness should reflect that (which this does).