Is $7,500 to replace subfloor on the main level a fair price?

I am replacing an engineered hardwood floor with white oak select 4” on two stories of my house. My contractor removed the existing flooring on the top story, which was glued to OSB and damaged the subfloor during removal. I accepted the recommendation to replace that subfloor. I am now facing a similar issue on the main level, where removing the existing flooring is likely to damage the subfloor. My home is higher-end, and I want a beautiful result, but I'm not enthusiastic about spending an additional $7500. I am also considering the alternative of laying the new white oak on top of the existing flooring, which would raise the floor height, requiring sanding down one door, raising the toilet flange, and resulting in shorter baseboards, though appliance heights would remain okay. Humidity is an issue where I live in the south. I am seeking opinions on installing new flooring over old and whether my contractor should have anticipated these subfloor problems. Update: It appears the builder used different glue on the main level, and the flooring is now coming up easily without subfloor damage, so I'm hopeful this issue will resolve itself.