Sounds like pure conjecture, here.
Remember that this was an army that held soldiers accountable for each and every round of ammunition in their cartridge boxes, and fined them 25 cents for each cartridge lost or expended outside the line of duty. Weapons were inspected in detail at least every Sunday, and deficiencies (like the loss of a sight) noted for correction.
The P1853 and P1858 Enfields were probably some of the finest battle rifles of the time, serving the Queen's armies well, and a favorite of both the Federal and Confederate troops. And I might mention that these same Enfields are soldiering on today in the hands of the Afghans.
I've packed an Enfield through some pretty intense reenacting usage for the past six years, and have not had any trouble with the sights; and the sights on the repro weapons are a lot flimsier than those on the originals. As any infantryman knows, you take care of your rifle, and it will take care of you.