This was true in Germany and the Scandinavian countries until recently, as well as in Switzerland (which has an Obamacare-like mandatory private health insurance rather than a single-payer system).
As soon as you have a massive influx of foreigners with no sense of duty to the country or society, the system breaks down. The "social contract" where people agreed to work and pay taxes for state-sponsored social services becomes a system milked by immigrants. Then the native population follows the example, thinking "if they're parasites, I can be a parasite too."
This, fundamentally, is why the European social welfare system will collapse and why it would never work in the United States.
But on culturally homogenous and work ethic you are correct.
To be fair to the Germans, the majority of the Turkish "guest workers" they took in the 70s have imbibed the German work ethic
You can't include Switzerland in your ethnically homogenous society as that it isn't. Work-ethic wise yes, but ethnic, no
As to the final part you wrote about things breaking down, you aren't correct about all European countries - in Denmark for instance, immigrants welfare opportunities are cut heavily, so the loafers move on quickly to Sweden. Even Germany isn't that bad and Switzerland gives you welfare only if you have a history of putting money into the system
Finally, the "European social welfare system" doesn't exist - each nation's implementation is completely different from the other