Yes cynical endings are not good, i agree, but neither are goodie2shoe endings where you get a stupid plot armor lucky strike, achilles heel to bring down the antagonist or whatever else mcguffin/mary sue that just happens to find the way to clear the final battle & executes everything perfectly to deliver a expected outcome.
The market is oversaturated with these types of endings from all corners, hollywood, manga, comics, tvseries, everything is giving people some false illusion that "in the end goodguys win" wich is undoubtedly not true, from historical perspectives, wars, and whatever else source that is clear, history is written by the winners and thats about it, you can have the firebombing of dresden painted as a utopian achievement of murdering milions of civilians, nuking japan as a glorious achievement "against evil" and so on. In reality people are flawed, thats why Eren was appealing as a protagonist/antagonist with childish motivations that grows up and sees the reality of the world and what he must do to achieve peace for his own people/race(?).
Dark souls/ Berserk do not do those things you mention tho, they do not "learn from their past" and stop suffering, souls has perpetual death and sacrifice to try and keep the world going and it ends in nothingness without going to much into it.
There is no future in "souls universe", thats clear by the end of the third game´s dlc. We have to wait and see how miura does berserks ending,it does not feel like he will go for a good ending but who knows, hes getting old and his feels are catching up.
While berserk has not ended, its still a revenge story that goes way of the rails, nomather the characters personal motivations its still filled with hatred and sorrow, from all angles & everything is twisted and contorted in both narratives.
You still have the reoccuring godhand beeing choosen anew, the "hand of evil" is still continous, even with SK trying to fight it for thousands of years.
Everyone is twisted not my some outer sources but by their own character, and they represent themselfs as those twisted interpretations of their self image based on their sinfull desire.