A “Straw Vulcan” is a straw man used to show that emotion is better than logic. Traditionally, you have your ‘rational’ character who thinks perfectly ‘logically’, but then ends up running into trouble, having problems, or failing to achieve what they were trying to achieve.
These characters have a sort of fake rationality. They don’t fail because rationality failed, but because they aren’t actually being rational. Straw Vulcan rationality is not the same thing as actual rationality.