"better" is in the eye of the beholder. You can get very near equivalents to the rk3588 on the x86 side. N5105/N6005 are a pretty good match for CPU benchmarks and better GPU, better I/O (more PCIe), SO-DIMM slots, better software support. All for a similar costs. I got a Intel NUC Essential N5105 for $160 6 months ago (SSD/RAM were separate).

The RK3588 is a 4 big core 4 little core design, so throwing out 8 cores as a point of difference is kind of misleading. Yes, there are 4 extra small cores in there.

If you just want a small cheap system, used ebay systems are pretty hard to beat. J4125 class CPUs are an excellent choice. At this point "faster" is less important than "works" I think. And the RK3588 isn't even touching the price you can get a used J4125/J4105 for. $55 https://www.ebay.com/itm/115671002802

Claiming a J4125 is "big" and "noisy" is similarly misleading. J4125 is a 10W TDP. RK3588 is a 12W TDP. You can passively cool either. N5105 and N6005 are similar power profiles. My J4105 idles at 3-5W, runs proxmox with my firewall and a bunch of VMs for databases and servers. 32GB RAM.

I couldn't find a Rock5 with case and power supply for anywhere near $150, and not even a bare board with 8GB for that. Let alone your claimed $140 for the full package.

Then there's architecture... A lot of packages you can find off the shelf for x86 just aren't built for arm. It bites you in the random places and burns time. Lots of time. I've burned far too much time trying to make ARM servers work.