There is more than one type of paprika, using hot chilis or sweet plus you can make it smoky as well. Chili powder will vary but uses chili’s, cumin and garlic powder. Again you can find variation in terms of heat developed. Cayenne pepper is a hot and fiery pepper used in some of these mixes.
A good fajita seasoning will allow the smokiness of that history to come through alongside a fiery heat, smoked paprika and chili work best. It is important to let the fresh ingredients of the fajita come through as well, so a few background spices like cumin, garlic and coriander allow that.