Roddenberry seemed more open to scripts that were reflective of the time's human and social flaws during TOS than he was whilst still wielding influence over TNG. "Mudd's Women" is a particular case in my mind: the dilithum miners were Federation Citizens living a pretty harsh existence, but expected to become wealthy (hence Mudd's interest in them), both were things GR vigorously excised from TNG. Likewise, societies without troubles don't spawn counter-cultures like that depicted in "Way To Eden." Granted, it's extrapolation, but it suggests to me that GR might have been more open to scripts examining systemic flaws in his Future Earth during TOS production run.
Of course, when GR was producing TOS, it happened to be the latest show he'd created and steered, and he tried several others after. By the time TNG was greenlit, not only was ST more of a broadly accepted cultural phenom than it had been in original run, it was about the only egg in his basket, and he seemed much more protective of his golden goose than back when it was just the show he was working on for the moment.