@PlayX - YouTube videos are terrible sources to judge performance. Unless they tell you their full PC specs, all of their Dolphin settings, and their exact Dolphin revision, there's no way you could reasonably recreate their performance. If the user in the video was using an old Dolphin revision (pre-3.0 for example) that explains most of the problem right there. Older builds on lower end hardware tended to get decent performance. While recent revisions of Dolphin have been speeding up recently, relatively speaking it's more demanding on lower end hardware than old revisions.
As DJBarry thought, your CPU is simply too slow. MKWii is actually somewhat of a demanding game, both on the CPU and GPU (though your GPU should be sufficient most of the time, as long as your Internal Resolution and AA aren't too high).
As DJBarry thought, your CPU is simply too slow. MKWii is actually somewhat of a demanding game, both on the CPU and GPU (though your GPU should be sufficient most of the time, as long as your Internal Resolution and AA aren't too high).