In terms of desktops, at $500 the Xbox One X competes with our cheap gaming PC build guide. And for the price, the specs are pretty similar. Our rig has a 3GB GTX 1060, which is about on par with the power level described above (though with significantly less GDDR5 RAM, as mentioned). Our rig also doesn't account for the price of Windows, but the trade-off there is you get a fully-functioning PC, as opposed to the locked ecosystem of a console. And, of course, the ability to upgrade down the line.
Here's how Microsoft's $500 Xbox One X compares to a PC | PC Gamer
funny
Isn't that only comparing price? Their cheap PC build opens saying you'll get 30-60 fps at 1080p and can't really do 1440p/4k. Your link says they expect performance more in line with the $230-$299 RX580 'but better' as that's not a 4k gaming card either. (and then again, the $600 PC in your subsequent post 'The thing with this PC, though, is that it's most definitely not 4K-capable')
We're probably another video card revision from being able to build something that can do what the One X does, current cards need a price drop to hit that level of performance IMO.