Why do you think that if you pulled it further the structural limitation wouldn't matter? The horn delaminates when at all stressed....
Pulling a hornbow less than it should be equals poor performance. Backing it with boo limits how far you can pull it - also leading to poor performance.
All the effort that goes into a properly made hornbow would be wasted by using sub par materials. That is a path that isn't for me.
I notice you add provisos to your statement eg. if a good horn were chosen…..that's what is being said there aren't any horns that are good enough...…
If you really want to make a hornbow then at least start with materials that will make one
Water buffalo horn/maple/sinew. Proven combo.