My dad, who has dementia (hasn't been diagnosed as LBD, but my own research has me wondering if it is) , moved in with us two years ago, after we lost Mom. At that point, he was still functioning mostly independently and had just given up driving (voluntarily, thankfully!). Over the past two weeks, he has gradually been getting worse in his reasoning, remembering, and coherent communication, and hallucinations and paranoia have gradually increased. However, over the past two weeks, it seems as though each day brings a new problem or change. He has become mean and belligerent, complains about most everything, and accuses me of horrible things. I've come to dread each new day, wondering what new, awful change I'm in for. What is going on in his brain? How much worse can it get? Part of me wants him to plateau but most of me is just asking the Lord for mercy. As awful as it is for me and the rest of our family, I can only imagine how scary it must be for him.
My MIL is only a few years younger than your dad. She has a neurodegenerative illness and also is very frail. We try to keep her stress down. She does not have a definitive diagnosis because that can only be done in an autopsy of her brain. It took her years to get a working diagnosis. And it took at least another year to get her medications sorted out. All that was back when she was not frail and had hope that she had something curable.
What you are going through is so very difficult and painful. If your gut is telling you to back off from finding a label then that is the right thing and the most loving.
She had similar behavior with the hostility, mean temperament, confusion, etc. I'd ask about medication to help with his anxiety and/or depression. That made a huge improvement with my cousin and brought her much relief.
My own Dad ran into an issue with an urinary tract infection, for him he was seeing ants on the walls and in his food, and he was determined the ants were there. Antibiotics helped with this situation.