This is a very moot argument.
I have coded in both GL and DX (Privately and Commercially). Both of them do exactly the same (basic) things, just in different ways.
I have also coded applications/played games based on both API's using both ATI and nVidia cards. While both brands worked fine using both API's, the ATI cards do have, well, sloppy drivers. So the OP's problem is most likely caused by a dodgy driver. It's definitely not OpenGL that is to blame.
Yes, OpenGL was desiged more for the visualization and scientific bits, but it is as useful and as effective as DirectX for making games.
And consider the situation if there was no OpenGL. Without competition it would most likely lead to DirectX becoming fairly crap/ not being maintained, because why would you improve anything if there are no alternatives anyway?