Re-inforcing anon, parity between teams would generally be interpreted as equality, or at least almost equal, chances of any team beating any other team on a given night.
This season, top 3 teams have a win-loss record of 27-9 against the rest of the league. Clearly, the top three teams are a level above the other six, this season.
At present, there are 5 wins between 1st and 4th and 2 wins between 3rd and 4th. We're about 60% of the way through the season. At the same time last season, there were 2.5 wins between 1st and 4th and 2 wins between 3rd and 4th.
In 2017-18 there were 2 wins between 1st and 4th and 1 win between 3rd and 4th.
In 2016-17, there were 3 wins between 1st and 4th and 1 win between 3rd and 4th.
In 2015-16, there were 3 wins between 1st and 4th and 1.5 wins between 3rd and 4th.
In 2014-15, there were 3.5 wins between 1st and 4th and 3 wins between 3rd and 4th. This was back in the era of Perth and NZ dominance (they were the top 2 teams at this point in the season) when people complained about the parity issue in terms of the ongoing dominance of those two clubs.
I look at those stats and feel that there is a clear and large gap between the top three teams and the rest of the league. That may change over the rest of the season but both Sydney and Melbourne have the easiest draws to the end of the season of all teams in the league. Perth have one of the stronger draws remaining, which may restore some 'parity'. They look more vulnerable this season than I can remember them looking for a long time.