Some classes of 2D rendering are faster on the CPU, but not all, though.
But even if it is slower, there may be advantages of moving the rendering to the GPU, like leaving the CPU to do other stuff, less power usage overall, more RAM available, etc.
But even if it is slower, there may be advantages of moving the rendering to the GPU, like leaving the CPU to do other stuff, less power usage overall, more RAM available, etc.
The key word here is "forward rendering". There exists no forward rendering primitives on GPUs besides triangles.
Your doubts are entirely unfounded. Every mobile device uses Skia-style hybrid GPU/CPU rendering entirely due to performance, and power consumption didn't take a hit from it.
There's a question of why this hasn't also happened on desktop, but I think it's just because nobody cares if desktop GUI performance is garbage. It's not touch-driven, so it's less noticeable. It's not front & center on reviewer comparisons like it is/was for iOS vs. Android. And since so much is web-based, the number of commonly used GUI desktop apps has plummeted.
And on platforms where Cairo is relevant there's bigger problems in graphics than rendering speed anyway, like the abysmal state of composition foundations (aka, X11 still being so common and wayland being stuck in permanent not-quite-there).