I don't see this at all. In fact, I think you have this exactly backwards. The negative criticisms here are by men who see themselves as plain-speaking (writing

I don't see this at all. In fact, I think you have this exactly backwards. The negative criticisms here are by men who see themselves as plain-speaking (writing) commonsense types and see Melville's work as radical and unconventional. Literacy as a status symbol could only have meaning within a very small public sphere - in other words literacy was extremely high within the group that could be expected to do ANY reading AT ALL. There have always been people who write with deliberate obscurity to appear smarter but the language of these reviews and their concerns with language are entirely straightforward in terms of the standards of their day.