Yes, the source of enlightenment lies within but it must be detected or realized. Presently, there are deeply ingrained factors, also within us, which make this difficult. The yana are all about reducing these distracting factors so that we can tune in and detect.
The most frequent questions I hear are, Why tantra? Deities? Mantras? Sadhanas? Why not just dzogchen? Simplicity? Naturalness?
One of my answers is that if you are able to decrease or come close to eliminating your distracting factors, including the noise of conceptuality, then yes, you will be able to detect the candle flame of enlightenment within through dzogchen. But if distracting factors are too noisy, then you can use the tantric techniques of mahayoga and anuyoga. These methods create a huge bon fire which intensifies what we are trying to detect.
Both approaches work but what makes each one truly effective is receiving the blessings of the masters.