Tim, keep in mind these are just opinions.
I have not performed any "testing" to substantiate anything.
I believe the true advantage of horn or baleen on the belly of a bow would be with short bow designs…it’s going to take the compression.
I don’t shoot short bows well, so most of what I build is between 60-64”. In a bow of that length I believe it may increase durability, but again it’s just an opinion.
A well tillered bow with a belly of wood seems to last much longer then my interest in shooting one particular bow.
I know it’s been used as a backing, but I have never done so. It’s pretty hard to beat good bamboo as a backing I believe.