Let's break it down. $5000 entry-level. What's it have?
- 8-core Xeon W, 3.2GHz base/4.2GHz turbo. The only such 8-core Xeon now is the W-2145 with a price tag of a bit over $1100
- AMD Radeon Pro Vega 56. Radeon Pro costs about 2.5x as much as the consumer equivalents, and I think Vega Frontier Edition is an appropriate comparison here. $1000 gets you a Vega 64 clone, while Vega 56 had an MSRP of $400. Let's call it $700 then, the middle value, though you will be spending more in a custom system for the full functionality.
- 32GB of DDR4-2666. Not particularly fast or fancy, but it is ECC. PC Part Picker shows the cheapest such memory costing $10 per gigabyte, so call that $300 after rounding down for convenience.
- 1TB NVMe SSD. There's a chance this is crap, but Apple isn't known to cheap out on their storage. A Samsung 960 PRO is currently available for $620 and is not an improbable choice.
- 10GbE is the new hotness in networking. A Black Friday sale put one such NIC at $60 for a single-port controller, but typically they're around $150 and worth every penny for some users.
- Not one, not two, but four Thunderbolt 3 ports. Hard to tell what this would cost aftermarket, but I'm going to call it $200. That might not be right though, and if Apple is using separate PCIe x4 links per Tbolt port that will drive the cost up.
- 5K monitor. Here's a big one. Cheap examples I've found are $1000. Apple does not cheap out on the display.
- Now, if you're making a custom system, you'll need other parts too: SFF case, SFF motherboard, and power supply. $400 for good quality components.
Tally that up. A custom build that might emulate an iMac Pro's specs would set you back almost $4500, and you don't get to use OS X on it nor do you get the AIO form-factor.
So the Apple tax is a mere 10%, and that covers labor, quality control, OS installation, and the ability to use real UNIX. Seems like a fair price to me.
The price is fair for what your getting but the style over substance is what hurts it.
The AIO form factor is a hindrence for a true workstation. The lack of upgradability and the small enclosure space negatively impacts performance. In house servicing is going to be a hassle as well.
The Vega 56 pro here is even more nerfed than the consumer part. This card has a peak performance of 8.9tflops which is barely any more than fury x. A big step down from 13.1 tflop peak of the FE edition. Add in the 8gb of memory which is only rated at 400gb/s vs the 480gb/s and 16gb, and I think this card is worth 500 dollars at best. If the Vega frontier is 1000 dollars this is worth less than half of that if we look how much performance cost upgrade cost in this segment.
Having Vega in this thing which will continue for the next two years is another big issue since during that time, Nvidia will have rolled out Volta and it's successors. Volta makes vega look like garbage in professional applications.
Garbage is a strong word but when you look at the massive delta in performance, the word seems approriate. We are talking about a 8x speeds up in some tasks and generally and average above 200%. Considering the 5k base price that goes up to 13k for this imac, Volta would have been a good fit for this. Heck even titan xp looks more versatile because of it's often comparable openCL performance and the addition of Cuda compatibility. Considering the premium nature of these products, they should offer the best which in the professional space has been Nvidia for the last decade.