Is there an argument that the world would be a better place if it were divyed up into bigger, more radically different nations?

I don't know if it has a formal name, but there's certainly an argument to be made for decentralization of... well, just about everything. Hell, there's even an old adage. "Don't put all your eggs in one basket." I think the major world powers realize this, and already practice it. More on that later.

Let's take your idea one step beyond, and say that each individual system needs alternatives within the same class. So capitalism would need multiple "flavors" of itself to give its "users" a reasonable alternative. This would act as a safeguard against corruption, and the inevitable fall of empires.

(Warning, economics lesson ahead) The argument for decentralizing governmental powers comes back to capitalist economics. If a market only has one firm providing a service, that firm is considered as holding a monopoly. When the service they provide is "perfectly inelastic" (meaning a good/service is something that customers literally can not live without) a monopoly can set the price as high as they want, or charge customers more based on what they can afford.

In this context, a government is its own monopoly if the citizens don't have an alternative. Taxes and civic duties can be viewed as our prices, and the service they provide is citizenship.

Expanding on this just a bit more, governments can (and do) create their own micro-monopolies (local monopolies) when they restrict their citizens from leaving. This is akin to a town that has a walmart providing supplies, and no other stores. No one can afford to drive to the next town for groceries, so everyone is stuck buying from them.

But as you have noted, there is a problem with this system. In reality countries invade each other, restrict the movement of their citizens, and evolve from one system to another over time. So even if it was possible to enact this sort of world system, it would quickly evolve into something different without some grand authoritarian power enforcing the whole thing. And of course, authoritarian globalism would defeat the entire point, as that global government would itself evolve into something else over time.

In short, a small selection groups that hold common ideologies (countries), united by a few different philosophies (American/Russian/Chinese empires), all balanced against each other and working as world police (globalism), is pretty much what we already have.

Would it be better if, if you felt, for example, Anarcho-Communism, Primativism, or Fascism made more sense, there was a place you could move to and live under that sort of government?

I don't think so. Elections are essentially a substitute for war. A formalized bloodless coup. If you divvy up a large country into ideological safe spaces, you would get an actual war within a few decades.

That's sorta what Voluntaryism is about, except you don't have to move to a different nation or anything. When people are dissatisfied with their governments, they should just be able to individually switch to a different one on a whim. Or make their own if they'd like. Maybe even live without one if they're stupid and crazy.

The only reason it isn't already that way, is because governments usually command militaries. And when people start conspiring to abandon them, governments can use those militaries to suppress that. So unless the people pull off a successful revolution, nobody gets their regime change, and they all get really frustrated and angry.

And that's especially a problem in a democracy, because then the people start fighting each other over control of political offices. And all that anger and frustration keeps building up, forever, and leads to culture wars. And now here we are.

If the South had won the American Civil War there would likely still be considerable friction between the North and the South. I can't imagine that other nations would have a more amicable division.