The open radeon drivers were developed outside of ATi, using the (limited/sparse) documentation they were provided under extraordinarily strict NDA. As a result, we didn't have things like
Z Buffering in the drivers until this year. But despite that, the drivers were in a much better shape.
This discussion (which if you read the dri-devel thread, ended with the ATi guys saying "we're sorry. we'll do better") is happening because AMD's marketing department dictates that they keep as much of the driver closed and developed in-house as possible. They're completely opening the kernel driver, but every layer above that is planned to be closed. There will be a free Mesa/Xorg/Wayland stack developed by volunteers in parallel with the proprietary drivers, for those that actually want to use their computer and not experience kernel panics (at a performance cost, due to not having full documentation of the card). Oh yeah, the proprietary drivers haven't even begun support for Wayland yet, and probably won't for another year or two.
This is a step up from before, mind you; AMD's previous setup under fglrx was a closed-source kernel driver with binary blobs, which would usually require a recompile every time you upgraded your kernel. In addition, because their software team was insane, they would take a snapshot once a year of the mainline kernel/X11, and build against that instead of merging to the latest tree. This means that all distros would have to pin their kernel/Xorg packages to a specific version (again, a year out of date), otherwise you just plain wouldn't have accellerated video. Arch (and other rolling distros) got so fed up with it that they stopped building fglrx in their repository, forcing people to use the open radeon/si/hd drivers. You had to do a rather immense amount of voodoo (add third-party repository, pin xorg/kernel to ancient versions included only in that repository, downgrade packages) just to get them working. If there's an exploit in the kernel or xorg, tough. If you want to have system uptime measured in days/weeks/months, tough. If you want Xinerama (good multi-monitor that plays nice with xrandr) support, tough.
In comparison, this new situation is a lot better. AMD is at least playing nice with the kernel developers, and the development team has fought enough with the marketing department to embrace a semi-open development model, which is where this dri-devel discussion comes in. We also got a pretty good inside view of way that AMD develops drivers/hardware, and some amusing commentary by the dri-devel maintainers (including Intel employees) about how screwed-up AMD's internal culture is to produce these sorts of problems. For instance, their software team cannot communicate with the hardware team, because by the time the drivers are started, the hardware team has moved on to another card, and all the knowledge is pretty much lost/changed/irrelevant. This bears repeating: the hardware and drivers are developed separately and at different times.
The end result of the thread is that they're going to split this 100,000 lines of hardware abstraction into much smaller chunks and merge it piece by piece. Hopefully this means that AMDGPU will be worth using in Kernel 4.10 or 4.11, depending on how long it takes.
I'm still using intel's mesa/kernel drivers in my chromebook. Yes, tearing/panning is gross, but if I had to pick between Intel and AMD's code on my machine, it's a no-contest.