"least"? it's not least, it's "not at all" spicy, there's no capsaicin in bell peppers so while they're part of the same family of plants/fruits in scientific terms, in the world of cooking they might as well be considered an alien plant that has nothing to do with the others.

In French, we have a (generic, as in encompassing the whole family of plants) word specifically designating all members of the capsicum family that are spicy: Piments, so as to exclude Bell Peppers (which we call Poivron) from any conversation about this stuff.

Bell Peppers can be considered a main ingredient and focus (in weight) in a recipe, while the others are only ever used as spices.