How can you say that?
Being the only AFL team in a massive city is what underpins Sydney's support. To say it has little significance is absurd. It's fundamental to Sydney developing a following.
Did you not read a single thing I just wrote?
You implied that Sydney had the entire city to itself, and the ability to draw support from that entire city. That is DEFINITELY not the case, because most of the sport-following population of Sydney follow union and league, which prevents them from actively supporting the Swans. While these are still potential supporters, it's not like they're clean slates just looking for an AFL club to support.
The Swans realistically, short term, have just the AFL following population to recruit supporters from. While the league and union supporters might consider the Swans "their AFL team", that doesn't equate to attending games, buying memberships, etc. Sure, there are a minority that follow both leage/union and the Swans with passion, but these people are rare.
As I said, it has an influence, but it's not that big. You seem to think that the Swans have 4-5 million people to readily recruit from, and that's simply not the case. It will take a lot of time before these markets are properly opened.