I'm less than convinced that unsympathetic FAs allow seat poaching even kind of often on assigned seating flights. I'm pretty non-confrontational, and if someone poached rudely, I swear i'd leave a plane before being unfairly displaced, especially with a short connection. If it actually came to that, I'm quite sure I'd be well compensated by AA/DL for the issue.
I actually feel like WN puts their FAs in a difficult position, lacking an actual policy re: seat saving. I'd hate to mediate some of the situations I've read about here.