…how? It’s a game, that you play, with a first person perspective, and shoot guns. Unless you only use VATS, a mouse is going to be more comfortable for most people, myself definitely included.
I don’t use V.A.T.S. at all; never have. Getting a decent gun early game and going for headshots has served me well.
Not everyone considers “sitting upright or hunched over at a desk as if working” the most comfortable position to game in and it’s not like you need the extra precision of the mouse to enjoy a story-driven RPG like you do when playing a competitive FPS that’s only about precision and reaction time.
Not everyone considers controllers to be more comfortable for shooters than Mouse and Keyboard. New Vegas is a fantastic RPG, but the combat is that of an FPS. Maybe if I was doing a bunch of non-combat quests I would agree, but as someone who has played thousands of hours both ways, I prefer mouse and keyboard pretty greatly.
You can have your own preference, I think it’s a bit strange to call mine “wrong.”