The RPi Zero 2 W consumes ~ 0.6W when idling, and costs $15 new, or in the $25-30 range with a case and USB power adapter.
Obviously, Raspberry Pis, SFF boxes, workstations and rack mounted servers all occupy different niches (with some overlap). Anyone confidently stating that one could fully replace anther with no context of the workloads is wrong.
Speaking of my projects - the RPi is perfectly capable of working as a web crawler (at a page rate that may surprise you) as well as a media download client & transcoder (again, simultaneously transcoding a number of streams that may surprise you).
The reason I prefer mini-pc's over pi is the x86 architecture and possibility to add more RAM. For maximum flexibility, I mostly run my self-hosted services inside virtual machines that I manage with Proxmox, and pi isn't ideal for that. Admittedly I found even the mini-pc's too limited due to lack of space/pcie slots for a GPU, and ended up with a custom desktop build. That allows me to experiment with stuff like self-hosted AI, and game remotely. Support for ECC RAM and more SSD's was a big plus too.
So, indeed it all depends on what and how much you want to do with the machines.
My homelab includes 1L PCs and 1 U rackmounts (actual servers) - I appreciate what each brings to the table.
It could probably run a single-task relatively well, like PiHole or something, but otherwise it's in a completely different performance category. Like an order of magnitude.
So 6W idle for J5005 would put it on the same level of efficiency.