"perfect setup" depends on use....
but regardless, all my "good" ARs have
1) good 2-stage trigger
2) magpul MOE+ grip
3) BAD short throw safety (left side lever only)
4) BCM Mod 4 CH
5) VTAC 2 point sling (on guns that need em, not all uses need a sling)
6) free float barrel
7) Guns with defensive use in mind get a light (not needed on competition rifles)
8) Guns with defensive use in mind get back up irons (not needed on competition rifles)
Optics vary, again depending on use.
Barrel lengths vary, again depending on use (shorter is generally better, I try to keep the balance point as far back as possible).
I hedged whether to add silencer to the list.... heavy, makes the gun longer, but oh so nice to have. I guess I look at it more like the optics, depends on use.
-rvb
Oh I agree there is no Perfect do everything perfect AR, but I think you can get one to do a lot of things well. My setup is a culmination of what has worked over the years and what hasn't in the types of shooting I do the most. I do like your list, with maybe the exception of a free float rail, although nice I really haven't seen much difference in use over a standard handguard for a do all carbine. Now for a precision or SPR style setup I totally agree..
I'm the same way on barrel lengths, this pinned 14.5" is probably my favorite. I have a 10.5" SBR but 9/10 times I still seem to pull this one out of the same to take to course and shoot. I'm the same way regarding suppressors, I have the YHM QD mount pinned on this rifle incase I want to suppress it. I will say though normally I don't use the can much however...