I started with a Dr. Optic back in 2001, after seeing it in some Swiss or German gun magazine. I ran it with no BUIS. I started seeing videos of Kelly McCann running a Dr. on his Glock 19 with no BUIS, we both carried that way for years.
The race guns in IPSC carry red dots and no BUIS.
The BUIS make the learning curve much easier for most people.
I am having a P07 done by Cajun, it will wear it's stock front suppressor sight and a RMR with no rear sight.
If by chance the RMR goes out, so what. If I am in a string of fire at my Thursday night combat match RMR becomes big ghost ring and I finish the string. If it should go out in a real life situation, same as above.
Remember that the basic rule for a gun fight in the USA really haven't changed 3 shots, 3 yards, 3 seconds.
In Israel I have used a pistol both on and off duty and some of those were outside the rule of 3's as outlined above. But as of right now I still feel in the USA your chance of a gun fight is very very low and your chance of having to make a 25 meter or longer shot is even more dramatically lower.