>would have been smaller or fizzled without their patronage

this seems entire implausible. Many of the expressionist, surrealist or modernist artists were European refugees who fled fascism, the government apparently spent less on their efforts than an average regional election today costs, and expressionism still exists.

This is the American equivalent of one of those 'are the Chinese behind this' conspiracies every time anything Chinese starts to be popular. Governments who can't get things done for billions apparently suddenly can invent entire art forms with a few million bucks.

No doubt there were people who thought abstract art would make for good advertisement for American liberalism, but no they did not invent, steer or even meaningfully influence it