So, it’s kind of doing different things. Ballasts are reducing current to protect things. From the wikipedia article:
An electrical ballast is a device that limits the current through an electrical load. These are most often used when a load (such as an arc discharge) has its terminal voltage decline when current through the load increases. If such a device were connected to a constant-voltage power supply, it would draw an increasing amount of current until it is destroyed or causes the power supply to fail. To prevent this, a ballast provides a positive resistance or reactance that limits the current. The ballast provides for the proper operation of the negative-resistance device by limiting current.
A constant-voltage power supply used for a single-LED (such as these loose LEDs) is simply dropping the voltage to match the needs of the LED, but there’s no need to to add more than a resistor…and depending on the power supply and your particular circuit’s layout, there might not actually be any need for that resistor at all.
an LED driver, is typically some form of microcontroller. RBG and RBGW led’s are increasingly receiving digital control signals rather than being controlled by modifying it’s power supply. for example, NeoPixels which have to be driven by some type of microcontroller to get their full capability out. (for example a purpose built controller, or something like a feather or pi pico or arduino) for neopixels and similar sets, you’re controlling the individual brightness of the r, b and g LEDs (and the w,), as well as the over-all brightness of each pixel, all of them largely independently. (it’s as complicated and not complicated as you want. honest.)