Ha, I expressed similar observations about Wsan some years back, though I still like his writing.
His characters tend to be motivated by sex, and exhibit most of their personality through sex. From way back when Amber was being written.
Brint joins you because you walked past him and he had nothing better to do. Brienne doesn't really have any deeper motivation than tagging along and banging you.
Wsan doesn't take a lot of interest in fleshing his characters out beyond sex scenes. It's partially why Brienne doesn't do a lot for me; her only real personality traits is that she likes you, a lot.
Of course, imo he also writes the best sex scenes on the team, and that's why I'm here, so it evens out for me. But I do think his characters could stand to have more life to them.