I actually have a friend who took a clinic with Walter once. She said she didn't like him AT ALL because he was critical and not that gentle with the riders. However, as much as I love my friend dearly, she is very stiff and quite hard on her horse's mouth, yet she doesn't think so....so I don't believe you that Walter won't be "firm" about things at times. And I don't think he would lie about Linda doing nice things with her horse ;)
As far as Linda being stiff......omg, she is one of the least stiff riders I have ever seen. And Remmer is a VERY honest horse who will do *something* if he doesn't like something...and a stiff rider is one thing he does not tolorate. She was flowing with his motion, not bouncy, fluid, and Remmer was nice and quiet.
Quite honestly I think you're just pulling at things to pick on. Do you not want Linda to be successful with Walter and in dressage? Hmmm...