I think, Eric, that your question with regards to 12L14 was answered by yourself when you described other barrels as being tough on files and cutting dovetails and what not.
I've hand rifled quite a few barrels and the best that cut is 12L14. The worse is 4150, followed by 4140. The 1137 used by Green Mountain cut rifles very smooth. There was a time when I demonstrated rifling at some shows, one of them being the Ohio Deer & Turkey Expo. Oddly enough, at one show, not far from our booth was Tompson Center. Those guys spent more time at our booth watching and partaking in what we were doing than their own booth.
The TC guys told us how TC made barrels: button rifled as opposed to cut rifling. In pushing the button the barrel becomes so hard due to stress that it can shatter if dropped. The steel they used was 4150. To allieviate this brittle condition, the barrels were stacked in a very specific way and then cooked in an oven for a couple of days to reduce the stress and brittleness yet allow for a tough barrel.
I think, but I'm not sure, that the majority of modern blackpowder barrels are cut rifled. I think that by cut rifling (by hand) being a slower, steady process the internal stresses on a barrel don't show themselves (this is just a guess). I have seen a barrel made by a not-to-be mentioned well none maker warp severly when it was reemed by John Kleggy at Freindship (the barrel was straightened and re-rifled the following year). Seeing that, I have to believe that the warped barrel (after reeming) could have been cut rifled by force of hydraulics, that force being transformed to the barrel that though was straight (before being reemed out) was now bent and warped.
It could be said, regardless of how the barrel is made and rifled, there will always be a few that have some sort of imperfection unseen by the naked eye. We as people can't control everything.
But as far as finish work on a barrel is concerned, yes 12L14 is great to wrok with, engraves nice, files nice, takes to browning well. If the end user isn't paying attention to what he or she is doing in the loading and firing process and blows their hand off or kills themselves, then Darwin was correct. Makes you wonder how much is user error as opposed to equipment failure.