The thinner sole, plus pre-worn leading edge I believe both account for this. The thinner CB sole allows it to get thru the turf better than the Pros, especially in the short irons, from my experience.
I haven't gamed the C723's, but I did have the C721's in the bag for a while and they held up quite well. I'll be following to see how they play for you!
Hitting the XT soft with a lot of wedges lately, and it's been a good experience. I think it has a good feel, but not as soft as I was expecting. It's by no means a hard feeling ball, but I guess when I hear soft I expect a bit more plush feeling at impact. Feels more similar to the Condor...