Except on the heel if you have too many fibers connecting the bowl and outside surface.It's difficult to compare briar to pine because of the differences of density and silica content. But I would say yes, straight grains are proven scientifically superior (just because it will make peoples head explode lol)
Ironically, the heel is often the thinnest part of the bowl and Straight Grain makes that point the most susceptible to heat transfer.