there are alot of variables ,, it really depends on the grain of the board,,
yes sinew would be stronger than rawhide,, as far as holding something together
if the board has good grain,, rawhide will hold,, so it just depends
if you have the board and can post a pic,, you will get suggestions on how to proceed,,
a good red oak board can be made with no backing, and other woods as well,,,
I have never made an osage board bow so cant give you advice on that,, i have rawhide backed osage board with success,,
sinew backing is a little advanced process,, its like cooking,, no one can really explain how they do it,, exactly