I feel like I am in a very similar boat. My wife is very strong willed and amazing at arguing. She will and is walking all over me at the moment and I feel constantly criticised and picked on. If I try and be assertive I am argued with, if I don't i feel like I am gaining no respect. It's very exhausting, so I admire you having the ba!!s to give it a go.
I also find that my wife likes to argue her point. I think a lot of it is just her expressing things that she never exposed before. I think that there has been a lot of stuff she has bottled over the years and now it is all coming out. And it comes out in very painful statements, accusations and conduct.
Many times, I don't agree with everything that she says, but I know it is pointless and actually harmful to argue with her. She is actually telling me how she feels. Who am I to tell her that what she feels is incorrect? It's how she feels! And, if you think about it, if I'm arguing with her over how I believe that what she feels or thinks is or isn't correct, I'm not on her side. I'm her adversary.
What our spouses really want is someone who believes in them, 100%. Someone who accepts them as they are. They have been hurt by us and are expressing their pain. Somehow, we need to allow them to let it out without letting it crush us in the process. We need to be the one they turn to when they are looking for a safe harbor. And yes, it's much easier said than done, especially when what they say hurts so much.