another way to put it is, in general, if you look at the AFL for a long time, the difference between the 'top' teams and an average team, is, basically around 20 points
(Essendon notwithstanding) - would have to look up my research on average to bottom - but in that situation you are relying on 'not so good teams' to both score and defend, which is tough - e.g. the Geelong and Swans deals this week as 'obvious' examples fo this situation - not taking into account other factors. Good team vs average team at home, have to add on a bit for the HFA of course.
As an historical note - Hawthorn were close to 30 for their bigtime period, speaking of freak teams.
and the league is more even with teams with much less depth due to stupid team list sizes
and one other quirk - scoring for the opposition can be a valid defensive option in footy, this is almost never the case in any other sport - especially sports that are incredibly low scoring like American Football, Rugby League, soccer, etc.
here's the current list
RATINGS LADDER
Essendon 39.93
Carlton 25.79
Port Adelaide 18.08
Brisbane 11.95
Melbourne 6.99
Hawthorn 3.96
Sydney -0.12
Adelaide -0.30
Western Bulldogs -0.74
Kangaroos -0.79
Richmond -1.49
Collingwood -3.28
Geelong -6.66
St. Kilda -25.16
Fremantle -31.43
West Coast -36.84
-- ignoring the bombers, as a statistical freak (scumbags) Carlton and Port are your standard 'top class' teams currently. West Coast is also an aberration at the opposite end currently, some of the worst football being played ever - or for many years, at least.