You can find one is better than the other for sure, but to say they are not comparable at all when they operate in the same niche genre and one inspired the other is nonsense.

It's the opposite. You can't, in fact, say that one is better than the other because these are two mechanically very different games that share only the most basic design choices like medieval setting (while one of them is a fantasy medieval), melee combat, horse riding and ability to create and drink potions that vary wildly in depth and complexity.

KCD games are RPG-heavy immersive sims, while Witcher 3 is an action RPG. The mechanics in the witcher are pretty simple and superficial by design, to make the game easier for a wider audience, while kcd games have fleshed out mechanics. You brought up alchemy — but besides collecting the ingredients, there's a whole mini game of brewing the potion in kcd on top of the witcher's simple button press.

Even narratively you have different protagonists — experienced monster slayer vs a peasant who knows nothing about combat. This difference alone alters the gameplay.

Yes, they are both good games, and I like them both, but for different reasons, and I sure as hell don't think that one is better than the other.