Where do you think that GDP per capita growth came from? The economy benefited immensely from those factories and access to cheap stuff on international markets.
Salaries are low because there is not enough high paying job, because there are not enough high-skilled workers to attract/fund businesses that would employ them.
Furthermore, the Hungarian economy and demography suffers from the same problems as other developed economies. Technological improvements made a lot of mid-value jobs so efficient (via automation and of course through global institutions and multinational organizations), that the demand for them disappeared. See David Autor's seminal paper: https://economics.mit.edu/files/11563 (for example page 13, figure 2 is very telling. middle class jobs "disappeared").
Hungary, just as the US suffers from the problem of transforming labor markets (middle class jobs are hard to find, plus typical worker class male dominated fields are shrinking, whereas female dominated service oriented sectors are rising). And whereas in case of the US a lot of people are simply caught in a vicious cycle of poverty and incarceration, about two hundred thousand Hungarians left the country since 2010. (That of course did not help the active population ratio, though people working abroad send a lot of money back.)
The education system is also regressing in the last 5-10 years, now the research institutions are in upheaval too, due to centralization and inefficient restructuring by the government.
This will slowly swing back one way or another. The recent "overtime work hours" law is a good example, because it doesn't make much difference, as the labor market for low-skilled workers is in a gridlock. (A friend of mine works as a HR manager and they can't find enough local workers, so they recruit Ukrainian foreign workers, for a simple, but big warehouse, 1000+ workers.)
And don't forget, wages will rise when labor share of profits increases, but that means more competition, less government protected oligarchs.
Privatization resulted in a lot of foreign companies owning stuff, not commies and informants.
Secret police driven businesses were not particularly successful even back then, they haven't accumulated much capital. There are bound to be some folks living off that, but investors in the early 90s were usually high income individuals. (Doctors, company directors, etc.) They got there during the 80s, which of course required the right party signals, but these people then sold stuff (real estate, companies, etc.) after its value appreciated to foreigners or the new guard.
It's very unlikely that "everything [in Hungary] is still mostly owned by communists and police informants."