Well if we don´t look only at the settings, I think that Witcher 3 is the most comparable as it also focuses mainly on main story and good, entertaining side quests in fairly realistic looking and believable open world. (As Witcher world is basically middle age society if all the past legends and rumours people believed at the time really existed)
Also assasin´s creed could have lot of similarities (realistic game worlds, history events and characters), even tho combat and overall story is vastly different.
I see VERY LITTLE similarities in Chivalry and M&B. M&B has medieval weapons and horses and they both are open world - thats where all similarities end. There is none other similar thing between those in my opinion. Their openwordliness is completely different. Combat may look similar, but as I tried both extensively, they in the end feel vastly different (you can attack from multiple angles and do some basic tricks, but thats all, as M&B doesn´t even try to be realistic).
Chivalry is even worse, as there aren´t even those fcking horses And combat is even more different (and even less realistic - reverse overhead swings anyone?)
Skyrim is interesting contender - combat wise absolutely different, settings is quite similar except for fantasy stuff, but it is much less story and characters focused, and more "freedom over everything".
I see 0 Dark souls in KCD, except for potential hardcoreness of fights (but this is just speculation as we don´t know how hard the fights will be).
If I had to pick, in my opinion KCD will be something between W3 and Assasin´s creed, just with less fantasy, more history and realism, and first person only. I suspect that you will have most similar experiences with those two gameplay wise - you will mainly follow main story, enjoying good characters and only sidetracking for quests and mby loot occasionally while enjoying fair amount of intersting combat and activities. All other games usually play quite different (more exploration and/or combat focused)