I think the negative sentiment expressed here is not fully in line with what old gunmakers thought about back-action locks. I collect primarily out of Kentucky, but work with rifles from all over, with a preference for Southern and Midwestern rifles. I have not seen a majority of broken rifles [through wrist or through lock plate mortise] that were back-action locks, and from my experience I do not believe they were more prone to breakage; it probably tips the other way from what I've seen.
In Kentucky, the back-action lock was perceived by the better gunmakers as a superior lock, based on the rapid switch to back-action locks by many of the better makers in the larger cities. The superior Bardstown rifles by Jacob Rizer and David Weller went rather quickly to back-action locks soon after the flint era ended in Kentucky. Louisville's best makers, Moses Dickson and Joseph Griffith, both used many back-action locks on better rifles. Benjamin Mills, arguably one of the finest target rifle builders in the United States, and highly admired within Kentucky by most other gunsmiths, went to back-action locks for almost all of his superior rifles after the flint era. There were obviously preferences in some areas for the older front action locks, by both gunsmiths and customers, just as there were preferences for longer barrels well into the percussion era in Kentucky, or preferences for flint guns well into the 1840s in the southeastern hill country, etc. etc.
In my experience with these old rifles, many superior builders considered them an advancement over the front action percussion lock in the first 10 to 15 years of the percussion era. I have never read of any old gunsmith's reasons for preferring the back-action, or even the front action for those who stayed with them. But today's collectors generally do not like the look of a back-action lock in a gun...probably because it looks so different from the old flintlock image...and because they can't pretend their percussion rifle may have been a flintlock if it's mounted with a back-action lock. We shouldn't let our modern dislike for back-action locks [based mostly on appearance] make us start believing they were an inferior style of lock. I don't believe the old gunsmiths who used them thought of them that way. Shelby Gallien