This group was all about Realism. Any experimental literature brought into the group would induce immediate wheezing and severe sinus pain. Their whole philosophy was: no reality is unimportant enough to be eliminated from the pages of our favorite books.
They especially liked scenes of workers schlepping their exhausted bodies home along dusty paths after long days working in the fields. Objectivity was what it was all about, so don't tell them what any one worker was thinking or feeling, got it? They only want to know about the social and historical forces at work.
Have you ever had a teacher trot out the old saw: "Don't tell; show"? Well, that's what this motley crew was all about. Don't tell them someone was a wayward bourgeois; give them a sketch of what life is like for that wayward bourgeois.
If this group believed in heroes, their hero would have to be Thomas Mann. He just "got" the whole Realist thing. You may be thinking that Marxists are a bunch of crazy revolutionaries, but this group of Marxist literary critics held up Mann because he kept to tradition when the big trend was to crank out super dense and complicated narratives (see Djuna Barnes's Nightwood if you must have an example). Mann wasn't afraid to mad-dog reality and all of its messy, well, realities.
Sure, Balzac was a Royalist (which is sort of like being the mortal enemy of Marxism), but so dedicated was this group to Realist aesthetics that it did not care about the personal political positions of its members. Now, Balzac's society may not have been this group's society, but society is pretty much society, right?
The funny thing is that Royalists and Marxists do have something in common: they both kept a hawk's eye on the social-climbing bourgeoisie. Balzac didn't write in order to make a power grab; he wrote because he was interested in the dramatic social change happening around him. If he wants to like kings, that's between him and himself.
Lukács was a natural for this position. When it came to Realism, he was like a junkyard dog with a meaty bone. He offered extemporaneous lectures on nineteenth-century novels, and he liked to think outside of the Realist box, which had a tendency to tick off Marxists and non-Marxists alike. He also weathered juvenile—and deadly serious—name-calling: people called him a revisionist, a misinterpreter, an idealist, and some things we can't quote here 'cause we kiss our mothers with these mouths.