“Is there any concrete proof that everything the Meforshim and Mussar Seforim say is directly from the Torah? “
No.
In fact, one can seriously argue that there is disproof because different Meforshim often explictly and emphatically disagree with one another. For example Rashi and Ramban can’t both be right about the sequence of the Torah narrative.
That doesn’t mean that we don’t take all of them seriously, even the inconvenient ones.