Yes, I think so too.
Yes I think so too. I'm familiar with the idea you mentioned about appropriate anger.
Yes, there's often a lot of placating the pwBPD by the caregiver. Personally—I think there's more just trying to stay afloat sometimes rather than be angry. Anger is pretty tiring too. It's quite off-putting as well. There's the old shortcut that I'm sure quite a few of us nons here are familiar with—when we see someone doing a lot of something, e.g., physical abuse, anger tantrums, over-drinking, spousal abuse, it seems quite natural to try go the "immediate opposite" direction to whatever negative thing we're perceiving. I can see a similar thing with the anger—e.g., the BP is so violently angry, therefore I need to be excessively giving/complicit/peaceful because "I'm nothing like that".
I'm more familiar with that kind of reaction in a family system, but my experience was a bit resembling that, looking back. If the relationship was like a boat, then my ex seemed to bring a heap of aggression to the boat of the relationship, and there wasn't any more room for me to have my say. A lot of things seemed to be that way.
Of course, here on detaching/learning, there's a lot of people who have heaps of anger. And probably appropriately so if you look at it from the Aristotelian lens. I think it's a difficult one to manage because anger is often more destructive than constructive—and yes while detachment involves destruction of the togetherness connection in a way—it's important to have some bottom line for ourselves for our anger and move forward in whatever areas of grieving we're each at.
Moreover if people aren't following a grieving stage framework (many people don't)—then it's easy to get stuck in the anger/attacking area and not go on to the constructive things like introspection and creative action.
Same here. I think the more years out—the more these feelings are like passing tides. Glad to be of company.

I remember, I was at a beckon, her best friend was at her beckon, her father and her mother. Anyone who wasn't was her enemy. She was angry so much of the time. It's interesting how they need the attention of everyone around. Anger is an interesting emotion. If it leads you, it's destructive, but it's also gives a ton of energy. The first year into the breakup, I used to punch a punching bag at the gym. Now though, I just talk about it and try feel it. Glad to be of like minded company too.