If I was buying the new Mac Pro I would get it with the 76 core GPU and 192GB unified RAM which makes it $9,599. To get the DIY workstation up to par with a 36 core Xeon W9-3475X, 128 GB DDR5 ECC RAM, and a Radeon Pro W7900 with 48 GB VRAM pushes it to about $10,705. The PC workstation would be faster, but costs more and can't run macOS. The Mac Pro besides being non-upgradeable is a better buy.
The Newegg DIY workstation is pretty much exactly what Puget Systems is offering with the same ASUS motherboard, except they don't offer the Radeon Pro GPUs, only Nvidia. Their price with the same 36 core Xeon and a RTX 4070 Ti is $10,717 with a 1000W PSU. So the DIY workstation is a better buy if you're going the PC route. It also looks like Puget Systems uses the exact same case I added to my Newegg cart, the "Fractal Design Define 7 XL Black Brushed Aluminum / Steel E-ATX Silent Modular Full Tower Computer Case."