There are lots of things that have been accomplished in the USA that would not have been if each of the 50 states operated as separation nations. Besides the obvious of the scientific and medical advancements, the common rules for business across states allows for products and many services to flow mostly uninhibited by each states rules (some exceptions apply).

Having enough resources as a single nation allowed for a common defense which saved the USA a number of times. Apparently this is also one of the reasons some regions of the world fell to colonialism because the various groups that occupied the land were not unified in their goals or defense. It allowed stronger powers to pick of each smaller group separately until the region as a whole was conquered.

I often times wonder if it would be better managed with more of an EU style system where certain standards are core across all states and then leave each country to truly govern themselves.

I like Europe a lot, but they've got some problems directly stemming from the lack of a single nation encompassing all of them. Even to-date there is not a single monetary policy in the EU. This lead to things like the GREXIT crisis. The leadership in Brussels can also get stymied by a single contrarian member halting progress such as Hungary frequently stopping aid to Ukraine.

None of this is to say the USA is perfect or the EU is flawed. There are positives and negatives to both systems. No one has found a perfect system yet.