Ok guys I had a chance to look today.
The house is a 2 story frame home build in 1935 (maybe older) with a tin roof. I went under there today and all looks good 2X10 joists on 16" centers but the span is 16'.
I think the problem is the old tub was recessed 3/4" below the hardwood floor, the carpenter put down 3/4" plywood and was trying to put the tub on top. He did not have anywhere to hide the gap.
The room does have a bit of a slope, but it was more like 3/4" not an 1.5"
We talked and I think he just has to work with it, the floor is not going to be level. I don't think the floor was ever level.
Nothing in the house is square or level.
That is just how old homes are.