Buddhism at its core is non-dogmatic. It has a number of precepts and principles, but does not ask its practitioners to believe anything in particular. Because of that, when Buddhism expands into a new region, it tends to absorb elements of whatever beliefs already existed in that region, because those beliefs become a bridge between old understandings and new ones. Thus, when Buddhism moved into China it absorbed elements of Daoism; when it moved into Japan it absorbed elements of Shinto; when it moved into Tibet if absorbed elements of Bön; and now that it is moving into the West it is absorbing elements of both Christianity and secular philosophy.
This doesn't mean that Buddhism is better or worse than any of these. It merely means that Buddhism uses the language and understandings of the region it enters in order to express itself more clearly. Most Buddhists will refer to this trend as the creation of a new 'wheel' of Buddhism, with the understanding that one wheel is much like another in the end.
Tibetan Buddhism styles itself as Vajryana (literally, the 'lightning path') on the claim that one can achieve rapid (e.g., in this lifetime) enlightenment. This boils down to a difference in style. Theravada schools focus on a slow, steady process of release through deep meditation, like watching and waiting for a pool of water to become still. Mahayana schools add in a component of service as bodhisattva, but still retain the essentially passive meditation model. But Tibetan Buddhism uses the structures and symbolism of the Bön mythology to actively confront and dispel attachments.
Whether this actually works as advertised is an open question. I have no evidence that Vajrayana teachings produce more enlightened beings per capita than Mahayana or Theravada, and I suspect the difference is more a matter of taste and inclination than anything else. Certainly other schools of Buddhism worry that the active model of Vajryana entails a risk that practitioners will form new attachments through that active desire for immediate enlightenment, but Vajrayanans will counter that the risk is justified by the potentials of the practice. In the end we all have to rely on our one capacity to (as the saying goes) separate the wheat from the chaff.