You're using AE 2015. It's a broken, alpha state (pre beta) version of an intention, not a finished product.
AE 2015 does not have multi-core rendering. Yes, you read that right. And I'm not joking.
Go back to AE 2014.
btw if you're at all interested in learning how a nodal UI works for compositing, and want something faster than any version of AE you've ever used, try BlackMagicFusion 8's beta build.
It's free, and should be for a while, cause it's a bit of a mountain to get over in terms of that UI paradigm.
But it's performant for compositing in a way you've always imagined compositing should be.
I've been having a lot of issues recently with AE CC 2015 (13.6.1) and PPro CC 2015.1 (9.1.0 174 Build) related to GPU, rendering performance, and overall sluggishness. If I have both AE and PPro open at the same time, previews are dreadfully slow and sometimes get CUDA memory errors. I have to single-task everything. Stopped using dynamic link completely. Basically treating projects like AE and PPro are on two separate machines - render out of AE, close application, start PPro, drop in render, make adjustments, close application, restart AE... it's a complete waste of time.
System is a MacPro5,1 with NVIDIA GTX 680 (official Mac version) and OSX 10.11.2 - likely will "upgrade" to 10.11.3 soon... CUDA is up to date. Using NVIDIA web driver, but issue is happening the same (sometimes worse) with the Apple driver.
Also experiencing rendering artifacts when using GPU accelerated plugins and the Apple driver. Using the NVIDIA web driver fixes this substantially.
I'm also on the CS6 just worked boat, however this is a bigger problem. The under the hood issues need to be fixed. Performance needs to be addressed. RAM previews need to get back to "real time" with frame accurate speed/playback when doing a full "RAM Preview". I shouldn't need to render through the render queue and then preview animations in PPro just to see them in "normal" speed.
All your points are 100% accurate and well researched, and true.
But for one assumption - that Adobe cares about Mac users enough to attempt to do something about their problems on Mac for video editing, compositing, effects creation and motion graphics.
They're in a relationship with Microsoft that's more beneficial to them than anything they could dream of attaining with Apple, and there's a lot of "bad blood" between Adobe and Apple that predates the Flash saga by more than a decade, and will never be resolved.
Compounding these issues is a "profits first, consumers on subscriptions" mentality that says any and all monies that could be invested in software development and advances being siphoned off to the shareholders and marketing departments.