I'm not 100% sure but I think statistically Geelong and West Coast have the biggest home ground advantages.
Statistically in the AFL there are home ground advantages in the home and away season and in finals. These statistics indicate a net advantage for non Victorian clubs.
There's no statistical evidence that Victorian teams have an advantage over non Victorian teams in grand finals at the MCG.
I would suggest since teams developed full ground team defence zones, which was Clarkos cluster in 2008, only the Swans in 2012 and Eagles in 2018 have won from interstate and a big reason the Eagles win was they changed the dimensions of their home ground to be the same as the g.
I think if you look before that, the only underdog interstate teams to win the gf were the crows in 97 and 98, all other interstate winning teams were clearly the best team all year