Indeed. During the social democratic age, i.e. the few decades after WWII, GDP growth has been high and income inequality has been low so social democracy does work.
Voluntary markets is a great and compact term which implies that the basic needs are always satisfied, that some goods are produced outside of markets (with stuff like open-source software it becomes prevalent that people do indeed work for free once their basic needs are satisfied) but that markets are not forbidden.
On a sidenote, what I like about social democracy, except for the fact that it is clearly the best system, is that its basic idea is moderation. I once saw an interview with Bergman in which he said something along the lines of "the great thing about Swedish social democracy was that people who hated each other, capitalists and socialists, could sit at one table and work together".
Or take an important ingredient of social democracy demand-management. Keynes described his General Theory as "moderately conservative in its implications"
, Stiglitz pointed out that Keynes "save[d] capitalism from the capitalists
Not that there is anything inherently great about the idea of moderation, a golden middle and so on but at least to me there is something intuitive and natural about such a system.
I do not want to question that social democracy is an ideology, it has its axioms which you do not question and so on, but among political ideologies it is perhaps one of the most unideological and pragmatic ones.
That's precisely why I agree with your point that the UFP is social democratic. If it were anything else much more propaganda would float around.