GPU is more powerful, CPU is comparable. Similar power usage. OTOH RP4 doesn’t have builtin SSD, you need additional case, additional heat sink if you plan to actually use it for CPU, and it’s not x86. Some also take PCIe cards without extra boards/hacks. If you don’t need GPIO ports and just want a low power server/appliance then thin clients are still much better option. I use them for VoIP, HomeAssistant etc.

> Raspberry Pi 4

We can easily compare that on Linux with benchmarks. I'd say at the same price point for used x86, x86 is still much faster.