I thought two handed infantry were still only used as "shock" troops. You don't really have a lot of them but you used them in a pinch to slam into an entrenched position (like a pike wall). Obviously they are extremely effective, but really only for their first blow (the charge bonus should be tremendous). Shields weren't just good for warding off blows, they did help in warding off missile attacks. An infantryman holding a shield about a foot above his head/body can protect himself in a way that even a plated man holding a two-handed sword just cannot.