I used a Samsung galaxy core 2 to play DBZ Shin Budokai and Shin Budokai 2 doesn't had lag or bugs and working in 60fps, without 60fps could and put in 4xpsp continued working very well I was very impressed, the only graphic driver for this phone is Open GL.
I think it depends the game are you playing, for example: I have played 7th dragon 2020 and the game had better performance with Vulkan, but playing GTA Liberty City he got better with Open GL than Vulkan, of course one is over view and other is 3rd person and also have CPU and GPU gets better than others. (mine is a snapdragon) But many games I played with Vulkan was better than with Open GL. But the emulator is so optimized I can't talk if really have a difference of performance in some cases. I'm not specialized with graphic drivers codes or hardware just basic knowledge about these topics and many tests.