I honestly think that in that regard he's just poorly written. It's as if Tsukuda wanted to write him as being crazy over cooking that he forgot to add some more human aspect for his character.
Not only that, but most of the time he's just either doing dumb/funny faces or just being smug, but he's hardly ever shown, annoyed, displeased, frustrated, sad or whatnot.
It's like Tsukuda wanted to make him super confident that made Souma hard to relate at times. I understand him keeping his cool during hardship, but you would expect him to show some frustration, anger or just more emotion when one of his friends is in a pinch. Instead, he just states at the scene with a serious/poker face, and we hardly ever get to read his thoughts on the matter. It's usually someone else's input.
I mean, even characters who are written as being cool-headed like Jotaro lose their cool every now and then to show they're human. I think Souma needs that.
Mind you, I'm not saying he should become completely different and burst with emotion, but just show a bit more interest and involvement with the rest.