Federal systems are meant to be scalable. The US gov't might have its problems, but the land size it governs is not the source of these. If you needed proof of concept, there you go.
The US federal government is a perfect example. Remote - geographically, culturally, and financially - from the people it governs, it has continually eroded the freedoms and protections of the bill of rights, and has usurped the sovereign authority of the state governments.
The federal government has been a great success for those with the money to control it and bend its power to their will, but has been an absolute disaster for the vast number of ordinary Americans.
Federal systems are meant to be scalable. The US gov't might have its problems, but the land size it governs is not the source of these. If you needed proof of concept, there you go.