I can't speak for Wilhelm, but Gray was brought up and nurtured to a point that he was only about fighting. Fighting was pretty much his life, he didn't go around hanging with girls, or interracting with them. Training, fighting, becoming stronger, being someone who wanted to seek revenge for what someone did to his family, comrades, etc is what brought up most of his childhood. Even in later years, it was all about fighting and comradrie. So his inexperience is clear at this point in time, plus different mangakas portray characters feeling to one another in a different manner. It took Gray long, mainly because it's for building up and being used in shipping development.
Nevertheless, Gray has a lot more husband material than Wilhelm does imo, especially when he gets to know and feel comfortable with the girl more.
He's the type of guy where action does more of his feelings than the latter.
Plus right now, Gray has the husband material candidates, Good looker, has that fashion sense (when not stripping), charming, knows what's acceptable it is when it comes to speaking to a woman, etc, and also, because he's not old.