I hope you are using the term Marxism in its loosest sense wehn talking about FFVII.

Marx's ideas on capitalism had very specific tones, predictions and theories primarily retaining to communism and how it would be achieved.

FFVII had an evil corporation that ruled the world through monoplizing a valuable resource as well as military might.
This has nothing to do with Marxist theory apart from there being a giant corporation oppressing the workers.

And suggesting FFVII had any sort of radically "in-depth" character lineup is just plain laughable.