Underpowered where it really counts. The GPU is barely better than that in a Quest 3 (Adreno 750 in Steam Frame vs Adreno 740 in Quest 3,) and while the CPU is almost 250% better overall than what is in the Quest 3, CPU power hasn't really been the limiting factor in most VR games I've played, it has been the GPU, both in PCVR and in standalone devices.
I imagine thats why they've gone so far with the dual stream setup that can use the 6ghz dongle + your wifi for ultra low latency to a dedicated machine.