It is not only the OpenGL support that lags years behind in Mesa, but the performance can too. In none of these wide-range of OpenGL tests carried out natively under Linux did the modern Radeon Gallium3D driver on the Mobility Radeon X300 128MB GPU out-perform the Catalyst drivers from years ago. In some of the tests, even the pre-Orca Catalyst/fglrx Linux driver from early 2006 still outperform the open-source Radeon stack from six years later. With many of the tests, the ancient Catalyst drivers were multiple times faster than the R300 Gallium3D driver of today.
With the latest open-source code, the OpenGL rendering was also incorrect -- and not like Catalyst -- for some of the Linux tests.