That would not just be boorish, but also wrong: both Sweden and Morway (the two I just checked) have around 17% foreign-born residents, with more than half of those from outside the EU.
Rather the question is, does importing radically different cultures, and low skilled labor bear a cost on the welfare state.
This is a cost that is probably acceptable, and necessary, but we should keep an eye on the practical limits.
Norway has far more money to spend, and Finland has far lower foreign cultural migration, so they don't make fair examples.
The USA has historically chosen "more immigration, less social services" and Finland has chosen "less immigration, more social services". "More immigration, more social services" seems to be a hard sell. For whatever reason people generally seem turned off when a welfare state spends money on people who they feel aren't like them.
To me it is a problem of convincing voters to spend money, not lacking money to spend. Convincing voters seems easier in a homogeneous place (whatever it was immediately after WWII, there seems to be a strong "we are Finns" culture now).
70% of Finns are merely on the rolls of the Lutheran Church, which really only means that parents had their child baptised as a popular traditional ritual, not as a sign of devout belief. I would suggest that Christianity never penetrated the Finnish psyche as deep as certain other European states. In most Finnish communities the church is not a center of community life but simply a building that stands as a museum (in many localities there is no active church at all). Also, with the rise of the welfare state, Finns immediately abandoned the notion that the Lutheran Church has any significant role to play in the lives of the less fortunate. Finland’s state churches themselves have happily handed over almost all of their charitable role to the state.
And in that portion of the country which was traditionally Orthodox, support for the welfare state doesn’t noticeably differ from the Lutheran part.
If you want to claim that Finns make their welfare state work because of ethnic homogenity, that ethnic homogenity would have to be located somewhere else than religion.
I think their advantages are essentially fundamentally geographic but deeply counterintuitive. The Nordics counter intuively may have the "advantage" of a harsh climate which both aids defense and promotes "sincere" cooperation due to a force outside their control and long term planning and infastructure. Don't prepare for winter and it kills you.
Conceptuallly it is essentially an inverse resource curse where a disavantage has a positive impact. Of course there are other unspoken factors to their success. Like all nations the geographic distance to trading partners has influence on growth.
The harsh climate has forced these countries to adapt, otherwise you'd simply perish in the past. Finland, having no conceivable natural resources like Norway, was forced to adapt by building a few thriving industries and excellent infrastructure to facilitate them.
That's a huge difference with France/Belgium.
Norway 554.24 bbl/day per 1,000 people
United States 28.08 bbl/day per 1,000 people
The main advantage of Norway seems to be that they didn't give away their resources for pittances to private companies, but exploit them directly.
Drilling a 4km deep oil well out in the north sea in rough weather is very different from drilling 20 meters on land in Texas.
If you look at various American oil states. They have managed their oil wealth far more poorly than Norway. No sovereign wealth fund. Public system often underfunded and in poor condition. Look at Oklahoma e.g.
There are as many "blends" of crude as there are oil fields (about 160 blends according to wikipedia https://en.wikipedia.org/wiki/List_of_crude_oil_products). Some are "thicker" than others and that results in different products you can get from the crude you refine. Also, each crude requires a different setting in your refinery, and it is very costly and lengthy to change that setup.
Refineries in the US are for the most part set to heavy crude.
Guess what kind of crude the US get's from fracking?
. . .
It's not heavy crude.