Nope. The homogenous culture I am thinking of (not a fan of people telling me what I'm thinking) is a bunch of Scandinavians, or nearly so. Correct me if I'm wrong, certainly, but those five minorities you mention -- all of them are pretty Scandinavian. Finns. The Flemish. Or Sami that have been there for five millennia. Etc. On a far, far, far different order of magnitude of heterogeneity than the US, or I'd imagine, even France. A common refrain from anthropologists and so on to the people who point to Sweden as a utopia is that with a tiny and relatively homogenous population, it's a hell of a lot easier to be a utopia. They are correct.
In any case, importing skilled laborers (or indeed Jews, as history bears out) into an already healthy population is very different from having a wholesale different culture enter yours and, because of low birth rates, begin to replace it. That's not happening yet, but it could. And "immigration" isn't a carte blanche key to survival for Japan, as if the only problem is having enough bodies, never mind what their culture and beliefs are.
If we didn't have immigration we wouldn't be the country we are today.
Undoubtedly. That neither means that all immigrants are created equal nor that replacing all Swedes in a microsecond with a corresponding immigrant would fix the problem. Reduced to the absurd, surely you can see that doesn't make any sense.
EDIT: I'm not sure about the Roma. They've tended to be outliers throughout history. In any case, the number of Swedish Roma is miniscule.