@Saregama and @medgirl might have more insights on this topic than I have.
I often leave garlic our completely, for some recipes lately. Something is missing.
The recipe usually still tastes good. I would think it could be the same with Chiles and other pepper.
I was surprised how spicy one butter chicken I ordered was last year. I was expecting the sweet type that is common in pan Indian restaurants. It was a completely different dish, having a lot more Chile or other hot pepper added. It didn’t give me a fix for my Butter Chicken craving. I would think it works the other way, too, for spicy dishes that have the hot stuff left out.