The "Specialist" actually had a true MOS related specialty whereas a "hard striper" was able to lead troops no matter what (MOS) they were.
Examples of the speedies (the nickmane for Specialists) included every skill you could think of other than infantry (11B). You would have seen speedy 4 (and up) radio men, or cooks, or armorers, or mortarmen all in the same infantry company for example. The section and platoons would be led by a hard striper of appropriate rank (SSG or PSG).
I personally never held the rank of corporal because I was part of a heavy (4.2") mortar platoon at that time in my career and my slot called for a Specialist rank. I subsequently went to NCO Academy and my next promotion was to Sergeant in a scout platoon (light infantry). As a result of being a hard stripe NCO, I was able to move into other platoons (Anti-Tank, Anti-Aircraft, Rifle) and gain across the board experience in an infantry company. I think that helped me greatly to become a 1SG as I was able to relate to all the MOSs in my company.
I hate newspapermen. They come into camp and pick up their camp rumors and print them as facts. I regard them as spies, which in truth, they are.
Gen. W.T. Sherman