" it doesn't seem to be very upwardly mobile (you get taxed a lot so it's hard to accumulate capital when starting from mid level income for eg.)."

I don't think that's true. You can get free/cheap schooling and health care is always there for you. I would agree it's easier to move upward than in the US where it seems one of the big secrets for success is to have wealthy parents. Coming from Germany and now living in the US I am also not sure if the taxation in the US is that much lower when you add all taxes together. And if you or your partner has any serious health issue it's very likely that this will cost way more than any taxes you pay less.