Longbeards weren't Core until 7th, Hammerers had Stubborn which made them marginally better, plus the ability to take a Runic standard. 7th did away with 0-1 on Hammerers and moved Longbeards to Core. They also made Hammerers Stubborn all the time, not just when the General was in there. THAT perk changed, but I can't remember it right off the top of my head.

The big paradigm shift for Longbeards and Hammerers came from the movement from Special to Core, AND them being a unit upgrade rather than a different unit entry. Having a third of your regiments Immune to Panic and the other third Stubborn made for a rather unbudgeable center line.