If you look at those screens, however, Dolphin is running at 100% in both instances (the first where the FPS is 20 and the second where the FPS is 29). As long as the game speed is 100%, that means Dolphin is running as fast as a real GC would.
Wave Race is supposedly a 30 FPS game for NTSC and 25 FPS for PAL, but not every console game had a fixed FPS. The developers may have simply programmed the game to drop the frame rate at certain points. Keep in mind that Wave Race was among the earliest of GC games, so programmers probably did not yet know how to optimize their games for the platform. I would encourage you to view gamplay in Dolphin and on a real console (preferably in real life, not on YouTube if you can help it) to note any discrepancies.
But yes, your GPU is using an extremely low clock (less than 300MHz) which will cause issues even at low Internal Resolutions like 2x and even 1x.
Wave Race is supposedly a 30 FPS game for NTSC and 25 FPS for PAL, but not every console game had a fixed FPS. The developers may have simply programmed the game to drop the frame rate at certain points. Keep in mind that Wave Race was among the earliest of GC games, so programmers probably did not yet know how to optimize their games for the platform. I would encourage you to view gamplay in Dolphin and on a real console (preferably in real life, not on YouTube if you can help it) to note any discrepancies.
But yes, your GPU is using an extremely low clock (less than 300MHz) which will cause issues even at low Internal Resolutions like 2x and even 1x.