I just tried to find a screen that's comparable to the iMac (resolution 5210 x 2880 and wide gamut colour space), and those I did find actually were around $2000 (i. e. http://amzn.to/2iPC5SZ).
I also believe the price difference is magnified by the options you chose – Apple does indeed charge too much for additions like RAM. The base model, with the same 5k screen, only costs $2000.
All that's neither here nor there – if I'm spending 10h+/day with something, I'm not going to look too hard at the price. Just the difference in noise is worth a significant premium, not to mention macOS.
Note the potential extensive value for someone who needs a display they can use with multiple inputs or wants to keep it for the future... There's something different about a standalone display panel. Besides all said and done a custom build PC + 2x 4k panels can be bought for the same price range so why wouldn't you? Because Apple socks the psychology of scale and experience at you so the price is a bit easier of a pill to swallow alongside any other hang backs you may have: closed ecosystem of software, oh and hardware, questionable design changes re: battery life and touch bar in latest MBP, their pattern of designed obsolescence, insert gripe here but that's plenty for me to laughably head to the nearest Dell or Lenovo product when it comes to a laptop and entirely self built when it comes to PC.
Right now I have a thinkpad e560 with 1tb ssd, 16GB rip jaws ram, i76500u at 2.5ghz. Now I know this anecdote is not really the same as what is on the market now but I paid $1.2k, I have a blu-ray if I want it, extra ssd if I don't. Also card reader. And plenty of USB 2/3 and network and even a Fucking VGA out. It's just as fast as my last retina MBP, and I used the cash differece for 4k panel.
Why people upgrade so often is beyond me. Maybe it's a capitalism thing. This human race is fucked.
I also believe the price difference is magnified by the options you chose – Apple does indeed charge too much for additions like RAM. The base model, with the same 5k screen, only costs $2000.
All that's neither here nor there – if I'm spending 10h+/day with something, I'm not going to look too hard at the price. Just the difference in noise is worth a significant premium, not to mention macOS.
Edited: macOS :)