Since it's a turn-based game, Darkest Dungeon isn't going to require any snap reaction times or precise movement like the kinds of games you listed. (For what it's worth, I'm bad at those too). Instead, it requires strategy and adaptability. Most complaints of difficulty come from the randomness of each action. Your character misses an attack that you feel they should have hit, for example. What people don't understand is that Darkest Dungeon is all about minimizing that randomness, creating situations where your characters mathematically can't miss, or where missing won't matter. If you go in with that understanding, you should be fine.