Your observation that the shape of galaxies can be explained by plasma dynamics is correct, and not only for spiral bars, but for every observed regular configuration of galaxies. As an example, here is a "top down" view of two interacting Birkeland currents (currents traveling on plasma filaments), showing how the dynamics of their interaction can form a galactic shape:
I dabble in Astronomy like I do in everything else, such as History, Geology and Law, (and I make my money from Law) but I really only know enough to be a danger to myself and others.
But even back in 1979, it just seemed to me a logical explanation. The professor said that a magnetic field could not be strong enough to define the location of massive objects like stars. My point was that the field didn’t have to be that strong, only strong enough to “herd” the interstellar gas and dust into “clouds” that conformed to the magnetic field. The stars then formed where the gas was.
He still rejected the idea. I did get top grade in his class, though. And it was thoroughly enjoyable otherwise. In the first week, when the ditzy sorority girl asked if there were any stars between the earth and the moon, I knew I was in good shape.
I like this thread because I like seeing the posts of people like you who follow astronomy a lot more than my scattered time resources allow.