Keep Peter Dutton out? The Greens? Consider the seats the Bandt has explicitly said the Greens will target at the next election: Sydney, Macnamara, Wills, Cooper, Richmond. All Labor seats.

This is true.

I wouldn’t say they’re cannibalizing the nationally left party though, Labor is centre left at best and we don’t have a purely 2 party system like the US so a left wing party could easily run in coalition. Otherwise you could also make the case that the nats cannibalise the libs.

which it makes it easier for the right-wing party to become the largest grouping in Parliament and thus best-placed to form government

If neither major party has the numbers to form majority government next election then they will deal with a minor/independent to form government, the Green’s obtaining more seats means if Labor is serious about forming government they would have to deal with them.