It seems to me Beltran didn't understand anything about science fiction, so he didn't understand that the Maquis crap was a dead end dramatically. It locked Chakotay into being wrong most of the time. Also, he didn't understand that dropping Chakotay's Mechanical Magic Mushroom did to the nature of the character. A science fiction character who doesn't explore the science fiction inthe character is useless. Seska deballing Chakotay pretty much finished it off.
So, when he didn't get big scenes, he just tuned out.
As to Wang/Berman, wasn't it Biller who turned him down for the directing gig? There seems to have been some sort of friction, perhaps Mulgrew disliked Wang (whose Harry Kim persona is apparently totally acting) as a rather active young man. There was a suspension for tardiness but Wang wasn't getting lines and scenes for a long time before fourth season. Caretaker was probably his high point. It's not clear why he was listed in the main cast.