I have a problem with people who call grimdark fantasy more realistic than other types that still include buckets of blood and continuous mistreatment of the ladies. Bad stuff has been going down for the entire existence of humankind, elf kind, dwarf kind and any other kind you're going to find in your fantasy. Is it realistic? Sure, but only sometimes and only some ways.
I'm a Dragon. I've lived a long time. I've seen some shit you wouldn't believe.
But I've also seen a lot of happy, light and non-grim stuff happen too. I have actually been to weddings where everyone threw rose petals at the bride and groom at the end instead of succumbing to poison or having their spleens ripped out. Sometimes people who are betrothed to a prince from another kingdom actually end up liking the guy and they have a long and happy life together instead of being forced to do sketchy things their mothers never told them about for the entire army.
Grimdark is a relatively new term for two different things, I think.
Some people use it to replace the word gritty. Gritty fantasy is realistic because life is not always unicorns and flowing velvet robes that never seem to get dusty even though the guy's striding across the courtyard. You have people that have not washed in months. You have kings who really don't want to be kings. You have women who are forced to use sex as a tool and kids who have to beg on the streets. You have trauma and mental illness and angst and lack of confidence and a bunch of anger that is not righteous.
On the other hand, some people use grimdark to describe stuff that is only grim and only dark and the grimmer and the darker the better. (I have heard some people describe Game of Thrones like this.)
If anyone dares to be happy in this type of book or show, it is usually either fake, unwarranted and extremely short-lived. Love and romance? Nah… grimdark is about sex, frequently forced, betrayal, infidelity and incest (sickos). Only small children have hope, only the great pretenders have righteousness and pretty much no one ever tells the truth.
Do all these things happen? Of course they do. Like I said, I've seen some shit.
Do they all happen at once? And all the time? And without letting up for a second so someone could pick a flower or actually survive the trip to the next town?
This is where grimdark strays into the realm of finding itself the purpose of self-preservation rather than the actual goings-on in the genre piece. What I mean is, when they keep piling on the shit, it might just be to keep the grimdark definition firmly attached not because it's actually how things work.
Yes, yes, I know it's fantasy. But it must be the fantasy of some real piece of psychopathic shit if they think it should never let up.