Perhaps that works for Belgium. Having 3 main groups (French, German and Italian) also works for Switzerland. I don't know much about Belgium, but I do know Switzerland has more power in their cantons (which are like states/provinces) than the federal government. Most cantons have a clear majority and majority French, Italian and German cantons are mostly clustered together. That ensures they can handle their own affairs so those groups don't fight each other for supremacy in the federal government. In contrast, America has federal supremacy over states. Whether anyone likes that or not, that has to be factored in. Allowing a devoutly Catholic Hispanophone culture to grow is not pluralist, but dangerous as it will pose a challenge to largely Protestant Anglophone America.