Who cares what Martha is does? She keeps herself to herself. What she's not doing is maliciously selling a lie to her young audience to stroke her own ego and line her own pockets. She's not cosplaying as child genius who sacrifices her entire life to studying and academic achievement, 24 hours a day, 7 days a week, and sometimes longer. She's not selling an unattainable image that not even she can ever hope to live up to. She' not preoccupied daydreaming about being an 11 year old girl in her childhood bedroom. She ain't stealing charity money to buy herself overpriced Miss Patina dresses.
Most likely Marfa is doing absoloutely nothing productive with her life. It seems like she is perfectly content to waste all her time on her crappy little creative projects, get drunk with her friends every other night, and spend her parents money whenever and wherever she can. If that's what makes her happy, good for her. The problem with Ruby is not that she's a waste of space. TBH, I wish I could be a waste of space and never work a day in my life, too. The problem with Ruby is the pathological lying, the snobbishness, and the judgemental self-righteousness.
And the biggest sin of all, Ruby's not even happy doing it.