I've mentioned in the past that MD is one story being told twice. In different ways.

The story: It's not who you know, it's who you 'know'

First story: Betty and Rita. We want to believe that Betty will make it in Hollywood because she's talented. Is she really? She didn't seem to be when practicing with Rita - she's terrible (in fact, they both are). It wasn't until she used her sex appeal at her audition that she seemed 'worthy'. And then she 'moved up' (was taken to a great director's set). How did she get the audition in the first place? The person she knew, Aunt Ruth (who appears to be a successful Hollywood icon), got her an audition for a worthless film. But Linney takes her somewhere worthwhile after seeing her use her sex appeal.

And Rita? She'll get nowhere not only because she doesn't know anyone, but also because she doesn't 'know' anyone other than Betty.

Second story: Diane and Camilla. Camilla's using the people she 'knows' to get to the top. We see her reaping the rewards.

Diane doesn't 'know' anyone other than Camilla, and she's getting nowhere.
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After we see both stories, we feel that Betty is 'dream Hollywood' and Camilla is 'dirty Hollywood'. But are we correct? We know that little ol' innocent looking Betty used some dirty tricks to get ahead. And Camilla seems to be quite talented, as we see on the couch with Diane (in fact, they both are).

So in summary, the story is that it's who you 'know', not who you know. And it doesn't matter if you are talented (like they both were in part 2) or not (like they both were in part 1).

I think DL's telling us that it's all dirty, no matter how well you dress it.

I think it's very hard for people to be completely objective about their talent relative to others. Additionally, there probably is no harder profession to make it then becoming an accomplished Hollywood actor. What percent make it? Has to be less than 1 percent of 1 percent that become truly famous. So yeah, it that regard, MD is about Hollywood.