Re: "Mary Sue"... I don't like words being put in my mouth. Besides, the "Mary Sue" trope is far different of a classification (for one, it has more to do with the ease of overcoming obstacles rather than moral alignment) and has exposed to be entirely sexist in wider modern discourse. Let's not go there, please, especially in the broader context of Rian Johnson's association with the Star Wars films. It more or less destroys the conversation.
Beyond that - perhaps a broader contrast would be appreciated. If not complicating Marta, complicate Harlan. As is, he feels like a plot device, an all-knowing victim in the middle of it all. I don't know why he gives everything to Marta other than to serve the theme of the film. We can't have two characters that are do-gooders with hearts-of-gold.
But even further, ehhhh, I totally reject the New Money argument - there's plenty of self-made millionaires that entrench their identity into their success. Honestly, Harlan feels like a major exception. Why? No reason given.