Nope, they're not. And AMD drivers are usually better on macOS than nVidia's.
Here's the current problem:
AMD's current GPU lineup doesn't currently have a "High End". The 480 is their current "high performance" and it's on par with their flagship from 2 years ago (the 290x and 480 have nearly identical benchmarks).
Add into that, Apple hasn't used the high end part either. They're opting for mobile. In the MacBook Pro for example, they're using a mobile verson of the 455. Which is far slower and lower than the lowest Nvidia option right now (1050ti or higher). In every single benchmark a mobile 1050 ti will outperform a 455 from Radeon, which is based on Radeon's budget/entry GPU
this problem is further compounded by the technologies available for GPU Compute. OpenCL is open sourced based, and while it's cool and works well enough, it's less capable than CUDA. CUDA's problem is that it's not free, and Apple to develope for it would need to pay license to NVIDIA.
so Apple chose the cheapest option, uses low end GPU's and sticks to OpenCL so that they can keep an "open" platform, that they don't have to license.
the net result is that overall, Apple current offerings using AMD GPU's just cannot keep up with Nvidia's current offerings.
NOW, this is talking about iMacs, and if they can get over the "thinness" obsession, AND Vega finally offers high end GPU power from AMD, than this is all moot,
But currently, AMD's gpu's are not up to snuff with Nvidia.
Not in GPU compute. Not in Gaming.