In most uses, triangular stock is there to reinforce a joint. It's real value is in the area that borders the seam between the two plates.

Ever see anyone use triagular spruce? or any other hardwood? No? I don't think I ever did. And a lot of times, the stock used was medium balsa. No attempt at all to put real strong wood in because it really wasn't being put in to provide much other than joint seam reinforcement.