Realism in D&D, and fantasy fiction more broadly, IS difficult. Both because, well, FANTASY . . . but also because the real world is super complicated.
No, that's not the problem. The problem is, in the real world, technology and society are deeply intertwined, the size of the world is defined by the speed of travel and communication, and evolution, not wars between mythic gods in planes beyond, drives the development of everything. There are no sentient tree spirits, no "folk" who appear human, but whose soul and being are drawn from the magic of the river. No god has ever cried black tears that sprung up into a race of malevolent warmongers...or a race of flower-loving hippies...or a race of
anything. These things
don't exist. They
can't exist. There is not a "realistic" version of these things.
There is a huge gulf between simplifying the real and attempting to make the mythic realistic. I can do the former. Granted, if I proposed an RPG entitled, simply, The Thirteenth Century, and the setting and background information had simplified, but reasonably realistic descriptions of various 13th-century peoples on each continent, most people would be horrified by the content. It would certainly not be age-appropriate for any players born after 1600. That world and its people are shockingly alien to our own, which is the way it is because rapid technological developments led to global empires and wars, ultimately leading to the last few decades of US financial & military hegemony driving a high level of economic and cultural homogenization of humanity.
WotC's FR wants to have 21st-century homogenization with a premodern technological landscape. It wants its humanoids to be both evolutionary and mythic in origin. It wants a paleolithic tribe with living side-by-side with a Renaissance city, each somehow having military parity, and the inhabitants of both having moral and religious outlooks that 21st-century Americans can sympathize with. None of this makes any sense at all; it's self-contradictory nonsense. The problem isn't that it's too simple; the problem is that it's brainless.
You can't make 5e FR "realistic" any more than you could make a 7-year-old girl's stuffed animal tea party "realistic." How would a fuzzy frog in a princess dress
really behave at a tea party in Cinderella's castle? The answer is, that's an idiotic question...but it's still probably less idiotic than asking what Drow would really be like.