In some Feral Metal games, performance has increased quite a bit after game and/or macOS updates. This prompted me to redo some comparisons with windows.
Rise of the Tomb Raider is now faster on macOS than on Windows 1803 on my iMac equipped with the radeon 580 and the core i5.
In fact, I'm getting an average of 71 fps on macOS on the benchmark tool vs 61 fps on Windows DX12 (57 fps with DX11). I'm using relatively recent crimson drivers on Windows, and the same "high" settings on both OSes (I disabled tessellation on Windows since it's not available on macOS) at 2048*1152.
The performance delta reflects actual gameplay (checked during the first level).
I also tested Hitman, and performance is basically the same between OSes.
Note that the OS and games are installed on an external USB 3.1 SSD for Windows, vs the fusion drive for macOS. I don't think this makes a difference in fps. If anything, loading takes longer on macOS.
Conclusions: Feral are awesome, but we knew that already. Metal isn't bad either.
EDIT:
Something isn't right on Windows. Actually, 2048*1152 isn't available (it's the resolution I use for this game on macOS). The game only proposes 2048*1536, which doesn't make sense since it's not the screen aspect ratio. So I suspect the game wasn't running at the same resolution on Windows. Curiously, 2048*1536 is more pixels than 1440p, though the games run a bit more slowly at 1440p on Windows. At 1440p, macOS is actually 10% slower than DX12.
At 1080p, macOS is only only a couple of fps slower.
So, not a victory for macOS, but we're making progress still.