4 cores vs. 12. When building apps, typically, there's a whole bunch of files that can be compiled independently before the whole shebang is linked together and - given enough RAM and fast HD access - a 12 core machine can compile these 12 at a time. The amount of data read/written isn't huge c.f. media work, so the access times for lots of simultaneous files is more important than data rate, and even SATA-based SSDs are good at that.
Photoshop etc. can take advantage of the dual GPUs in the nMP for image processing, and media work involving few huge files (rather than lots of small files) will benefit from the high-bandwidth PCIe SSD.
Basically, the nMP was optimised for pro media work rather than general heavy lifting.
You've got that back to front. It is beneficial for third party hardware manufacturers to make sure their hardware works with Windows and produce drivers etc. If Apple wants hardware (esp. internal hardware rather than peripherals) to support Macs they pretty much have to write and support the drivers themselves, or persuade the makers to add support. That's probably why they're reluctant to support hardware too far back (if you don't test on it, its not supported).
NB: Bit of perspective - I'm still using 10.9 because I've got a couple of things that don't support 10.10 and later. Its no big deal and I'm still getting security updates. It will be a few years before your 10.11-max machines become doorstops. If Apple don't come up with any hardware that tickles your upgrade bone before then, then its Linux/Windows time.