Costner will go to his grave trying his hardest to prove he isn't milquetoast, but he'll never get there.
He's just too fucking dull, predictable and unoriginal.
He was great in the baseball movies and I liked his Tatonka dance, but he's done nothing memorable since.
You could add Elliot Ness.
I think he has shoehorned the same character into every role. It's a likeable guy and worked really well there for a while, just like you said.