You are mistaken. Specialists saw and still see combat. A Specialist is merely the same pay grade in a non-NCO position. As I mentioned in that thread, there are no Specialists other than E-4s anymore. So an E-4 can be either a Corporal if they are an NCO or a Specialist if they are not. What makes an NCO? Many things, but to put it simply, an NCO is in a formal position to direct troops - a Specialist is not. When there were multiple grades of Specialists the idea was that the individual would be in that rank to enable them to attain a higher pay grade and have some professional development. For example, a very senior medic might be a Specialist E-7. When Specialists went up to E-9 (yes briefly) there was the NCO grade of Sergeant Major and the NCO grade opposite the Specialist E-8 was of course, the First Sergeant. These ranks didn't last long. Quite correctly, the Army felt that anybody who had attained the level of an E-8 or E-9 deserved to be an NCO. So the rank of Command Sergeant Major was created for E-9s who directed troops and those who did not were Staff Sergeant Majors. Likewise, the old rank of Master Sergeant was resurected for E-8s who were not in formal positions of directing troops. Some ten or more years later the Army came to the same conclusion about E-7s, E-6s, and E-5s except in their cases there was felt no need to differentiate and they all became "hard stripe" NCOs. That is, Sergeant First Classes, Staff Sergeants, and Sergeants. So why was the E-4 version kept? Most likely because the Army just didn't need that many more NCOs. Corporals became a rarity and for awhile there in the 1980s it was thought they'd disappear altogether. Only infantry and MP units had Corporals. Time passed and NCO needs changed and now there are many Corporals once again. So will the final Specialist grade now go away? Not likely. It's still a useful demarcation.