> I similarly like nationalism because it helps preserve distinct cultures
That's not what nationalism does, though. In the sense of liberatory and separatist movements (e.g. Catalonian, Scottish, Kurdish), sure, but in the more common sense (e.g. Russian, German, British) it's an oppressive collectivist movement that actually tries to eliminate local cultural diversity by imposing a rigid interpretation of "the national culture" and suppressing any deviation from it. Even in seemingly homogeneous European countries you have language minorities (not just dialects: e.g. Sorbs/Wends are a group native to Germany but culturally distinct and speaking a different language in addition to German, which is imposed as the national language).
I think what you describe sounds more like what Democratic Confederalism strives to do, i.e. form bottom-up self-governing groups via a system of delegation and confederation. This doesn't require a state (which "nationalism" usually implies, often with strong authoritarian undertones in the name of protectionism) and it doesn't require top-down control. Democratic Confederalism is actually best suited for regions that are culturally heterogeneous and would pose difficulties for central governments (e.g. Lebanon, which went out of its way to force a proportional political representation of Christianity and the two major Islamic traditions in order to do justice to its distinct religious-cultural minorities but still ended up with Hezbollah).
Ultimately it's not a lack of "nationalism" that is creating global cultural homogeneity but the commercialization and commodification of culture: Hawaiian religious practices are converted into generic Tiki torches and flower garlands made in China and sold at Walmart, German Karneval and Oktoberfest become beer binges and so on. Local customs are sanitized, decontextualized, synthesized and replicated as a commodity until the original is lost and only the copy remains and has become interchangeable. This is what "cultural appropriation" originally means: creating a no-name knock-off version of someone else's culture and selling it as a commodity, often resulting in the knock-off existing beside the original in direct competition and eliminating it through the power of the market (because a focus group tested sanitized plastic version will easily outcompete the original).