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I don't know if raw numbers is really a good way to look at the problem.
The US system is also deliberately designed to be much different than the Australian system of government, specifically there's a focus (or at least a pretense) at federalism in the US system that isn't (to my knowledge) mirrored in the Australian system.
That means more bodies which should (in theory) allow power to be spread out rather than concentrated.
The US also has, effectively, 65 (50 states + 14 territories + DC) mini countries within itself that all need to do things. Australia has (IIRC) seven states. The complexity level is much, much higher in the case of the US.
Rather than too many I think it's probably better to point to how free these agencies are to act as a bigger problem.
For instance, the ATF (Bureau of Alcohol, Tobacco, and Firearms) has been embroiled in a pretty big controversy lately regarding the definition of certain types of firearms that are legal to own in the US. By changing how it defined a particular legal term the ATF has been able to effectively make new things illegal.
This is a power the ATF is not supposed to have, they are an enforcement agency and do not have the power to make new rules per how the US system is set up but by changing existing rules (something that has a far lower standard) they can essentially "create" new rules. 
On a wider scale, you have law enforcement agencies getting caught in a wide variety of instances doing things like lying to the media, fabricating a scare ("rainbow fentanyl"), and an assortment of other  examples of coloring outside the lines and the response is...pretty minimal.
The 2020 uprisings were rife with a wide range of abuses by a number of agencies and the fallout from that has been essentially nothing. The police fired so much tear gas in Portland that they poisoned part of the local water supply and kicked off a ruling from a federal judge restricting the use of tear gas. That ruling was largely ignored.
Politically these agencies are immune from almost any form of attack (the exception being the ATF, for obvious reasons.) Anyone politically speaking ill of law enforcement in any way can expect a shellacking in an election for not being "tough on crime."  
To me, that is more of a concern than there being too many agencies.
In my opinion, policing has huge issues with not enough oversight, not wisely spent budgets, and not nearly enough training and qualifications as European countries for example. However, I think the biggest issue is that our Social system does not have nearly enough money and there's expectation for the police to handle everything >

Yes. When every little town has its own police force and everyone has to handle all their own administrative matters, hiring, training, etc you create a lot of inefficiency, variability in standards and performance and reduce the ability to do oversight. >

What would be the solution to that problem?
Centralized training and administrative services for multiple localities? That would save some money. >

I am from New Jersey, the land of endless local government, and the result of endless local government is crazy levels of inefficiency which cause high property taxes and governments so small nobody even sees the corruption. 
The average American town is around 6000 people. That’s way to small to justify a police department. Either roll up a few towns with a single police department or handle it at the county level. Have standards, training and as much administration as possible handled at the state level with federal guidelines that must be met and a system for federal oversight. 
Maybe start treating the police as professionals and model things more like how we license doctors, lawyers, accountants and such. >

I upvoted you and I see some merit in your argument.
It seems, though, that big metroplitan areas are where we have most of the crime because that's where we have most of the people.
THOSE cops are overwhelmed. They need more officers, and they need other responders to take over some of the problems cops have thrown in their laps.
They also need stigma-free, mandatory psychotherapy. None of this "I can take it, I'm a tough guy." Objectively, police need community support as much as communities need service and protection.
Also, no more "code of silence" or "you can't touch me when I commit crimes. I got immunity and a union." We need to KICK OATHKEEPERS out of the police department. No more gang members "moonlighting" as police officers.
Do I support the police? Yeah. Do I support the KKK and white nationalist weirdos? NO. >

Yes, we should have one state police with divisions for cities and rural areas.  New York as an example would have a very large force with multiple divisions.  Montana would maybe have two divisions.  However all would be accountable to their state legislature; have standardized enforcement, training, complain procedures ect.  
That would give us 50 police agencies and something like 18 federal departments. Much easier to manage in my mind. >

The large number of agencies reflects the nation's political design and structure. We have a federal government with several law enforcement agencies. Then we have 50 separate states each with one or more state law enforcement agencies. Then we have separate forces in big cities and an independent sheriff in most every county or parish (Louisiana). Add that up and you have the large number you cite. Jurisdiction over cases can open a can of worms. Each agency has its own training process and content with often very little coordination. Police unions also seek to maintain each law enforcement agencies' independence. Separate data bases are maintained. Thank God the FBI has developed a single source of data for some evidence (e.g. fingerprints). But otherwise we have a law enforcement tower of Babel. The best first step at coordination, in my opinion, should start at the state level. Training standards, code of conduct requirements,  data collection and more must be directed by the state. But this will be difficult in huge cities like NY, Chicago, Los Angeles who want their own police for political rather than law enforcement reasons. >

Have you every heard a politician discuss the need for centralisation or more coordination at a minimum? Or does it fall into the too hard basket for them? >

Not often. I was heavily engaged in Los Angeles city government for over 20 years. I am a lawyer by training but pls don't hold it against me. As to your question, which is a good one, the answer is sometimes. The LA mayor and city council often tried to harmonize police deployment, training, etc with the LA County sheriff. But it was impossible. Maybe the geographic picture might help you see the complexity in LA. LA city is about 350 square miles with a population of over 4million. LA county is 4,000 square miles with an overall population of over 11million. There are about 88 cities within the County. Think of this like a huge piece of swiss cheese with the holes representing each city boundary and the solid areas the responsibility of the County. A number of small cities contract for the County Sheriff to be their law enforcement agency. But there are still roughly 65 cities with their own cops, including the city of Los Angeles. It just so happens and each city and county enjoy constitutional "police power' i.e. the power to maintain their own police force and other powers. So you get largely uncoordinated cops all over the county. It is a structural mess> Politicians view cops as necessary to cover their own ass. They do not get benefits from coordinating with other agencies. The state can change this with budgeted programs etc but state elected officials represent the various parts of this swiss cheese so nothing really happens. Full disclosure I taught some Urban Law sessions at UCLA law school many years ago. I hope this muddled picture helps you a bit. >

Wow very interesting insight! Thank you