Would the frequency of LED be equal to that of microcontroller
That's correct. The LED will flash at the same speed as you toggle the pin, which in turn will be related to the frequency of the microcontroller.

Everyone's confused because they know something that you don't - you can't change frequency just like that! No passive or active device can do it. You mention capacitance (doesn't really exist in a LED but let's go with it) and you're correct. They will only change the rise/fall times. If the capacitance gets too high, you will see an effect where the LED will not have time to rise up to the high level until the microcontroller tries to make it low again, causing all the "toggling" to disappear and you will eventually end up with a voltage in between low and high, with some ripple.

The device that affects the frequency is just the microcontroller and its oscillator.