The ACMA channel finder definitely echoes that! The only bits not available as "Good" are most of the range of block 25 and 26. There are little bits at the very bottom of 25 and very top of 26 that apparently work, but everything in-between is listed as "possible" with indoor use only recommended.
That is certainly the case for the suburb of Sydney, but it seems it varies a lot across the greater metropolitan area. Even Newtown, which is only a few kilometres from the centre of town has a pretty different listing on ACMA. The "likely" in blocks 22 and 23 changes to "possible", and a bunch of block 24 changes from "good" to "likely". ACMA suggests there is less ranges available in Newtown than the CBD.
North Sydney, a few kilometres in the opposite direction is entirely different again. It only lists channels 27, 34, 45 and 51 as good, which a whole bunch of 'likely', and a chunk of block 22 and all of 23 listed as 'possible'.
I suppose it raises a pretty good case for wide band transmitters and receivers!