It's that focusing on one specific aspect of the system and compromising on everything else that produces the really big discrepancies. I tried to use PCPartPicker to spec out a rough equivalent of a maxed-out Mac Pro in terms of CPU cores, GPU performance, and RAM and SSD capacity, but still ended up at with at most a 3.5x disparity, and that's ignoring the GPU VRAM capacity limitation and features like Thunderbolt and 10GbE and assembly and warranty and support. If you want to assign $0 value to a large portion of a Mac's features then you can make it look wildly overpriced, but that's mostly an admission that it's the wrong product for your needs.