Avadon 2 can be used with OpenGL without any additional work but as far as i remember the DX-version was faster and more stable...but this was years ago.
Overall, the problem is that DirectX is built around using Microsoft's COM, wich OpenGL can't use. OpenGL should work with all programming languages, if your're able to use C you can even make changes/personal adaptions and until 98 it was even faster but with modern graphic accelerators, a operating system designed to use DirectX and even a hardware designed to be used with windows...DirectX wins the race most the time.
I was told, if you use linux and/or are good using C to optimize, write your own software-mods OpenGL is better then DirectX but i have no personal experience with that.
Post edited June 26, 2019 by DF1871