It seems, out of that list, that Mesa has been doing the least over the past 8 years. I acknowledge the great achievements that have been made in the way of KMS, DRI2, GEM and so forth, but these projects and the way they disrupted development and developers have set Mesa back by many years, where progress was mostly stalled as developers waited for the memory manager and modesetting to take shape before they could work on 3d support. Then Gallium came and divided effort in half between the gallium and classic DRI drivers.
Gallium is a response to the lack of development power and the need to share code across all of Mesa.
DRI2/GEM/TTM are needed to move beyond OpenGL 1.5. It did not set back Mesa by many years, as Mesa couldn't move anywhere at all until DRI2/GEM/TTM were implemented.
OpenGL 2 is impossible between these things. They had to be done.
So if we are to compare kwin with say something like gnome-shell as equals, granted the g-s developers are probably being funded to work on this more, but still I get regular reports from the g-s devs in RH on what drivers do and don't work and what features are slow and missing, and we try and target Fedora releases to make sure that the g-s bits work on the shipping drivers.
The g-s guys understand the ecosystem they are working in, and work with it. The kwin guys seem to take 0 interest in working with a community. I've gotten driver patches from g-s guys, and never any contact from a kwin developer. Granted RH also would prefer that I make g-s work so it gets a higher priority than kwin or games.
The thing is if kwin wants to be a Linux desktop it needs to run on top of Linux, not some ideal of what Linux should be if we had 50 more developers writing graphics drivers. Its called reality and generally living in it makes for a better quality of product.
...I was mistaken when I thought that audio would be a more showstopping issue for the Linux desktop than graphics. I was under the assumption that either the open drivers would catch up, or the proprietary drivers would support the same APIs the open drivers do (e.g. KMS). I was wrong on both counts. Audio problems have disappeared into the periphery for me; I rarely have any audio issues at all when using a modern Linux distro. But regardless of whether I'm using ATI's proprietary driver or the open drivers, I have always been disappointed by the graphics stack.
Graphics have historically been a weak spot of Linux. If anything, the last years have been much, much more successful for Linux then any previous point in history. You do have to consider that Linux has known many, many years where the NV driver was the only option if you wanted to do anything serious with your GPU.
Audio stack also hasn't caught up yet to Windows though...
*wishes more features
So if we are to compare kwin with say something like gnome-shell as equals
That's not quite right.
Gnome-shell includes the functionality from both Kwin and Plasma.
If Kwin developers are not checking for open drivers compatibility, then it's rather unfortunate. But they've done the same thing to the binary nvidia drivers when these were broken, so I don't think that it's a slight against the Mesa developers.
Well, apparentely, Kwin devs are enthusiasts working on their own machines, not some paid developers by Red Hat having probably access to various hardware, thus are able to test it personnaly.
Martin said in his blog that Kwin was trying to use functionnality advertised as supported, and that in fact it was not, making the fallbacks they have implemented useless. Since he doesn't have the equipment to test it, he obviously can't file bugs himself.
It's likely that KWin devs should try to get more reports on different platforms instead of assuming that everything works as the binary Nvidia drivers, but you can't also ask the two or three Kwin devs, who work on their own, to be able to match a paid dev team, moreover working for the same company as the driver developper.
I agree with Mr Bridgman approach, though. I assume Martin was on the defensive side with the bad reports coming with the KDE 4.5.X release, but blaming others is not constructive either.
Hopefully, some good will come out of this and many bugs, revealed by this release, will be identified and fixed.