Indeed, you are entirely correct. Why don't they transfer some files to offices other than Sydney? And why do immigration employees reply with a repetitive phrase (that each case is unique)? This response is empty talk because citizenship requests come after PR (Permanent Residency), and the former has been thoroughly audited a thousand times before being granted.
Therefore, obtaining citizenship is a result of an accomplished process and does not require new investigations, especially since the individual is present on Canadian soil; even if they commit a crime or similar actions, they would be recorded and easily identifiable within seconds. Thus, the arguments that each file requires a separate investigation are baseless.
The truth is that there is significant laziness and negligence among employees, specifically in the Sydney office. In other offices, people have obtained citizenship within just two months. The Ministry of Immigration should either transfer more staff to the Sydney office or redistribute the files to other offices. However, this situation is peculiar and unacceptable.