Like anything on here, its an opinion (based on personal observation) but I would cite last years GF series.
So your argument is that it happened once? That's not particularly convincing.
I remember having this discussion on OzHoops with somebody else, and looking at the NBA championship (because the NBL data isn't as readily available) teams, examining where they were compared to league average offensively and defensively in terms of points per possession.
The 2004 Pistons were the only team that wasn't elite at both ends of the floor. As far as I recall, from that field it was split pretty evenly between teams who were better offensively than defensively, and teams that were better defensively than offensively.
So basically, being a good team wins finals. Which really shouldn't be that hard to figure out.