Hi OP. I'm a therapist and I agree it is confusing. When I was a child, the scenes you describe were completely normal, everyday occurrences in my home and were perfectly legal: there was no protection in place and not even any acknowledgement that there was anything wrong with such abuse.
I therefore found it bewildering (and painful) during my therapy training, to discover that nowadays, thankfully, safeguarding protocols are in place not just to protect children from obvious, physical harm, but to protect them from the effects of witnessing abuse.
I do think that there's still too much a sexist tendency to put the responsibility (which can feel like blame) on the abused mothers in such circumstances. If a mother is unaware of the effects on her children of seeing her treated badly, interventions tend to be aimed at the mother rather than the abuser. However, this is done to ensure the mother is aware that the abuse she's experiencing is also affecting her children and that she takes steps to protect them.
More could be done to support mothers in such situations and help them protect themselves and their children. It's hard to have a clear picture of what boundaries are even possible or how very much better you deserve, when you're worn down with the effort of surviving abuse.
I hope your therapist is able to support you through this difficult time and that you're able to see it through to much happier new beginnings.