I think it's the other way around. We have alot of really nasty shit being pushed on us these days as "normal" and said shit is increasingly hard to swallow. Our stories are getting darker to reflect this fact, because we need characters we're able to relate to on some basic level.
The hope and optimism of the 1960s and 70s got a bit of a retread in TNG, but it's long since stopped resonating with viewers. For a lot of people, their daily existence is actually "I'm surrounded by people who think I'm an asshole, in a system designed to fuck me over, for a boss whose singular talent is covering his own ass, in a country that resents the fact that I've survived as long as I have." Star Trek is and has always been a product of the society that created if. If Discovery is dark and grim and unpleasant, it's because America has become a dark, grim and unpleasant place to live for a frighteningly large number of people. Some of those people want to see stories about how someone in a similar situation manages to overcome it and maybe improve their situation at least a little. That's the Catharsis implied in good fiction: it helps you process all those unpleasant and indigestible emotions of daily life without slipping into existential dread.