The competition convolutes their options giving the impression their prices are more competitive. Generally the performance is worse and thus value is worse.
Firstly not many (if any) manufacturers sell 2tb PCIe SSD configurations. So there isn't much basis for comparison to that at all. It was tough finding manufacturers that even offered 1tb PCIe SSDs in their AIOs. Regardless we shouldn't get upset about the price of something no one else offers.
If we look at Dell for example, pick out their best AIO XPS 27
model for around 2850 dollars you get a 512gb PCIe SSD with no larger options available. You can build a Mac with better specs cheaper. Go down to the
2750 dollar model and you get the options for 1tb PCIe SSD for 570 dollars + the price of 2tb 5400 with 32gb m.sata SSD (what is replaced to upgrade to an SSD). Apple charges 500 dollars + 2tb Fusion (128gb PCIe SSD + 7200rpm HDD). So you give up more but pay less for Apple which I would consider a wash overall. However lets keep in mind the stock option for that Dell is a MUCH slower SSD and a slower HDD and is basically more expensive.
Adding more convolution to the madness they call a computer line up many models are offered with SATA SSDs (instead of PCIe SSDs) which are considerably cheaper and slower.
HP is similar. Looking at their
27" models their storage options vary quite a bit. Ranging from 1tb 5400rpm HDDs to 256gb PCIe SSDs with 1tb 7200rpm HDDs also offering 1tb SSHDs which are basically slower Fusion Drives using 24gb SATA SSD portions and 5400rpm HDD portions. Most of the HDDs are 5400rpm and many of their SSDs are not PCIe SSDs.
Moving away from AIOs to desktops to something like Alienware (sorry I know this is Dell but its supposedly higher end) and you can get a
model that comes standard with a 512gb PCIe SSD + 4tb 5400rpm HDD however it cost 5399 dollars. Upgrading from the standard storage option only gets you more 5400rpm HDDs in varying capacities. Goto models below that and it looks to be all SATA SSDs and 5400rpm options i.e. slower than iMac options.
Honestly all the above options are junk IMO, either they don't offer better/larger SSD options, charge more, and/or just don't perform as well. We need to just keep in mind PCIe SSDs are just expensive. If you bought similar performing PCIe SSDs yourself for 2tb, 1tb, and 512gb you would spend approximately 1200, 600-500, 300 dollars respectively. Apple charges 1400, 600, 200 + the cost of the 2tb Fusion drive that is removed for the SSD. Obviously those prices will vary but I wouldn't consider them too terribly unreasonable.
I imagine there are manufactures out there that clearly offer a lot more for less however I doubt there are too many. Maybe you know some off the top of your head?