Really, it does not take that long to have $4k tied up in an AR. My 10 inch MRP with Comp M3 and KAC mount, KAC front and rear BUIS, KAC trigger, KAC VHG and rail covers, and my still awaiting stamp, NT4 comes close to that. I am waiting on my SR-15 to get delivered. I think that it is going to wear an ACOG. The fact is, this hobby is not cheap. I don't get the impression that he is trying to justify it or brag about it, just that he ran the numbers. He probably did not realize how much he had in it totally if he built it up bit by bit. We have all been there. Sure you can buy several rifles for what he has in that one. Clearly that is not how he chose to spend his money. I'm into NFA stuff, I could buy lots and lots of cheap ARs or AKs for what some of this stuff costs. That is not how I choose to spend my money. The point is, who cares how this other guy spends his money? I'm pretty sure that the only one in this thread affected by the OP's spending habits is the OP.
Also, who cares if has had a bunch of combat training with it? I may be in the minority, but my firearms are by-in-large toys. I keep a shotgun in my bedroom and I wear a pistol pretty much all the time. I have taken a couple of basic defensive pistol classes but that is the extent of my serious firearm use. My ARs live in the safe. I bust them out and shoot about 500 or so rounds per month purely for fun. I don't do convoy or diplomat security training, I don't practice assaulting ships, and I don't own body armor with pouches for enough magazines for any engagement. I am a pilot, I fly airplanes for a living, I'm not a commando, and I act accordingly. It never ceases to amaze me that people will be an accountant or futures trader during the week, then spend the weekend learning how to transition to their sidearm with their weak arm because their strong arm and carbine were blown off by a grenade. That is all fine and good if you do that sort of thing for a living, or even for fun because you enjoy it, but don't deride those of us with less heroic and probably more realistic expectations of what we will be doing with our rifles. I suspect that the majority of gun owners are recreational gun owners, we do this for fun. It is a hobby, if you will.
Life is too short to be so serious about it!
Rob