I would argue that if you count the EU as a single country, it would be more decentralized than the United States. The EU would be a good example of a "working" confederacy (as a general, Confederacy member states are allowed the right to leave, where as Federation states are usually stuck). Additionally, members of the EU are allowed to engage in foreign relations with various nations of the world, where as if Texas starts having diplomatic talks with Russia, Texas Government has some serious issues.
In addition, the United Kingdom Commonwealth nations could be a looser form of devolution as all Commonwealth nations are independent countries that all have the same head of State (The Queen of England) though that would be a rather poor example of any kind of federalism as most of those countries did peaceably what the U.S. did in the Revolutionary War.
Federalism is generally seen as a good thing for large nations where the member state gives up some powers to a central government, but is allowed to keep other things. Yes, the U.S. is essentially 50 separate countries that collectively are negotiating with foreign powers as one voice, but don't want that same authority micromanaging. Nations with large areas such as the U.S., Australia, Canada, Russia (Both the USSR and the Modern Russian Federation), Brazil, Mexico, and India all use federalism to manage smaller regions that might have different needs when compared to one nation as a whole (Nebraska doesn't need a Navy and Alaska doesn't need a tax on Corn growth, to name some examples.). Most Federations leave International issues and issues between member states to the Federal Government and any issue that doesn't meet that threshold is restricted from the Federal Government (the entire point of the 10th Amendment of the United States Constitution is basically to stop the Federal Government from taking control of powers not discussed in the Constitution... those are powers of the state).
Perhaps Switzerland's federal government has even less power than the United States as the Cantons (State level regions) are able to set their own immigration policies and Swiss Direct Democracy extends to the Federal Level, where as the United States has no Federal Level Direct Democracy (though all 50 states have some level of direct democracy).
Edit: Oh, Federalism also does not require a Republic form of government. Malaysia is a Federal Monarchy and technically, so are the UK Commonwealths (they have a Queen as their head of State). Japan's Prefectures were based off of the Pre-Meiji Feudal divisions during the Shogunate.