I guess you are referring there to the Ars Technica benchmarks? Don't forget that they said themselves their numbers aren't completely to be trusted, since the benchmark suite they used was not yet properly optimised for Metal for Mac. Metal benchmarks for iOS consistently show a clear, albeit small increase in performance.
Now that mobile CPUs have continued to get faster, the lower overhead of the draw calls isn't really the limiting factor it once was. Now it's more about driver/shader efficiency. Some latest benchmarks on iOS for example have shown that OpenGL is actually producing better frame times than Metal is now that the CPU draw call batching isn't the limiting factor.
https://gfxbench.com/compare.jsp?be...S&api2=metal&hwtype2=GPU&hwname2=Apple+A9+GPU
Granted this is a single benchmark suite, but it's the only one that is consistently performed on most mobile hardware. 3D Applications on OS X are rarely CPU limited. A mass majority of applications that are being made to support prior generational APIs (prior to DirectX 12 and Vulkan) will not push graphics in this way. Unless there are benchmarks/applications that truly push the draw call overheads there is rarely a situation where Metal is going to drive the performance over previous generation APIs.
When an application is made to push these draw call overhead you get some great performance gains as documented here.
http://flexmonkey.blogspot.com/2015/09/a-first-look-at-metal-performance-on.html
There just aren't a lot of applications that have that extreme level of draw calls because it doesn't have a prayer of running on older hardware at an acceptable frame rate. Only brand new software such as the the Ashes of Singularity benchmark/game will actually push these new API to where their lower overhead actually significantly benefits the framerate.
http://www.eurogamer.net/articles/digitalfoundry-2015-ashes-of-the-singularity-dx12-benchmark-tested
Until these types of applications are the norm, the Metal API isn't going to benefit that much on OS X. It is nice that they are future-proofing for when that day arrives, but that's a couple years from now before applications are designed for these low-overhead APIs, at least for Windows/OS X. Metal is now available on a good chunk of iOS devices and for iOS-only releases, this might be a better test bed for applications to utilize the new low-overhead APIs into their visuals/design.
When Metal was first announced for OS X, there was hope had by myself that Apple's sub-par OpenGL drivers could be eliminated and a more efficient Metal driver set could be used. However, early reports are showing that Metal drivers are not more efficient, and in some cases worse than OpenGL rendering the same scene. If that scene was redone to push the driver overhead like the samples done above, then you would get performance improvements that Apple touted.
Anyways, my point is that traditional draw-call conscious application rendering is not going to benefit when the CPU is not the limiting factor. This is currently is the case in a vast majority of cases for OS X applications in the next couple years.
