Dolphin does support quad cores, it just utilizes two cores of it and three when you're using LLE and have LLE on thread enabled.
You can see that the CPU utilization is 50%, which means two of the four cores is on load by Dolphin.
That doesn't mean you'll see two cores perfectly on load all the time while the others are doing nothing unless they're locked to the cores, which they are not.
Since the CPU load gets scheduled amongst the cores by the OS, the reading you're seeing is correct.
You can see that the CPU utilization is 50%, which means two of the four cores is on load by Dolphin.
That doesn't mean you'll see two cores perfectly on load all the time while the others are doing nothing unless they're locked to the cores, which they are not.
Since the CPU load gets scheduled amongst the cores by the OS, the reading you're seeing is correct.