For sport it makes sense. It can be cheaper, it can be a challenge.
If you were doing something that prioritized field shooting at UKD in varying light conditions you would not be nearly effective with iron sights.
I think you would have benefitted from going through our SDM course back in the day. Before TRADOC got their mits on our work. Not knocking you, no, several snipers did it in fact (it's fun and it was a different course from sniping). We did KD and UKD with irons and ACOG's and scored both using a NM scheme. I've got the benefit of seeing hundreds of AR's fired by hundreds of "expert" (40/40 army standard) shooters. I know what they can do and what they can't do and exactly what the differences are between irons and ACOG. IME? Not much. The ACOG is better for quickly engaging a target and quickly determining approx. distance without looking up, but that's it really. I can actually fine tune irons to suit the conditions better provided I have good dope to go on, but they're a bit slower. That's why we use a "battle zero" of 300m, in a nutshell.
Of course to get good irons you've got to "fix the drum". The rear sight drum is fixed for either a 20" or a 14.5" usually and of a particular twist. It's also setup primarily for 300m zeros. First thing is to take it apart reset the drum. Bottoming it out should be your new 100m zero. You can use plastic or laminated paper or whatever, and make new markings to put on that drum later, ones that will have YOUR x meter (or yard) zeroes. But that comes later, after you spend time collecting dope so you know enough about how it shoots in order to do that. The front sight is a bit easier, just use the A2 fixed front with a NM thin, square post. NM rear sight helps; if any play is left between the sight block and the handle, you can shim it out with thin metal shims. Some have more play than others. If this is an iron sight only weapon, don't skimp on the sights and consider using a "bloop tube" --a non-threaded barrel extension used to extend sight radius past the "point minimal returns" wrt to barrel length and velocity. These types of front sights can be very high speed and expensive. Don't forget to lamp black all front sight posts and rear apertures prior to use. They sell it in a can but a dirty candle works just as well, maybe better.
Front sight on rail vs. barrel: in short, tubes have a bit of play and it's better to have a true fixed front sight vs. mounting one on a rail. Just a fact. Same as with flip sights, they just aren't the same animal (though KAC flip sights can be zeroed pretty damn close and within 300m always get the job done for me).
IME, optics cause more problems than they solve in shooters that haven't mastered the fundamentals. Also, again in my experience, I've seen it that those that are proficient with irons have less problems with optics, but not the other way around. Irons is to walking as scopes are to running; you wanna walk before you run.
Having a rifle that's dedicated to irons isn't a bad idea, I was gonna build a NM service rifle and never got around to it. Don't have time to "do it all" in life, you know? But I learned more about shooting using irons, really USING them than I ever did with an optic. For example, you can't go from 200 back to 600 and NOT make significant changes based on prior shooting, wind, etc., and expect to group well. You just can't.
I feel the same way about dope books, leather shooting slings, a thick glove and a jacket or sleeve and proper positions too. Fundamentals. Shit I feel should be taught somewhere in middle or early high school.
Good luck! And talk to some NM shooters if you can, those guys know all the best gear and tricks to use with irons.
