They included a $1499 monitor in the list as well, along with a $400 VESA arm mount, and hundreds of more dollars in accessories.

Overall, with your Silicon Mechanics build they'd probably be closer to a $8000 build. On top of that, a P4000 is pretty much a beefed up GTX1060, which gets smoked by a GTX1080TI if one is going for GPU performance. They're not really comparable builds.