Not all woods are created equal. Having said that if you do a board build and use vertical grain, wouldn't one wood species work better if using flat grain..? All stave bows are built going with the grain.
I picked up a maple board which is flat grain, I know it will probably take more set, but should it not be more flexible.?
Building with oak flat grain is an issue where you have more lifting, splintering and grain run off.