A decent GPU on a desktop will destroy it, but that's not the point. The point is the power/performance ratio. The M1 hits this while barely getting warm, while the PC requires active cooling and uses 200+ watts. Put a 40Tflops PC GPU on your lap and it will brand a stamp of the laptop's bottom cover onto your thighs.
I gotta run the test on my desktop pc to decide how to feel about this.