Methinks you've just been exposed to easy single-player games, or choose not to challenge yourself enough... And that's to say nothing of Souls games.

I've 100%'ed Dark Souls, Dark Souls 2, Dark Souls 3, Bloodborne, and Sekiro. I still wouldn't consider any of them more satisfying than my average match of Dragon Ball FighterZ. Well, maybe Bloodborne is, but I haven't played it in a while so I wouldn't be able to say for sure.

Have you played a single player game where you go from nobody into a fearless demigod?

Like I mentioned in my post though, that's just the game giving your character power-ups. You as a player don't have to grow, which you usually don't unless you specifically try to and most singleplayer games aren't built with that style of play in mind. I want ME to be better, not the character I'm playing as to be stronger.