Even though it is extremely oversized, you answer the question with the pictures in the blog of how to conveniently install such a patch panel: First screw the patch panel further down to lay the cables, then move it up (or leave it down if the cables were fed in from below). Time required maybe one hour.
Keystone? For that money, you can also have an electrician do the work.
No, you’re not overlooking anything, I am also completely satisfied with my QNAP for end users. Wouldn’t know that I ever pushed the CPU to its limits. But to each their own.
The difference is that a 19" case fits much more cleverly into such a cabinet. That the performance of such a device built yourself costs only half and is upgradeable at will – power consumption almost identical. And if you like the software, just google xpenology. Works wonderfully here on a self-build (currently as a mini-tower, soon then 2U cases, e.g. Inter-Tech 2U-20240). Not pushing the CPU but using a NUC for this, a PI for that ... in my opinion that’s fiddling around, I just set up one more VM. Or you buy a 21U rack to place an HP Microserver on a shelf ...