Hi DD,
Thanks for your post. What is DS heart? Uprooting ignorance sounds like a very nice explanation to me. Regarding Mahayana views: Tantra is part of the Mahayana. The whole point in practicing Tantra is to realize the Prasangika view at the deepest level of mind. Only then we can truly overcome self-grasping and its imprints. If you ask why? Because it's been taught so. Joking! It also makes sense as there is no mention of deeper levels of mind in Sutra, and no mention on how to overcome ignorance at deeper levels of mind. So we need Tantra. If you ask for scriptural reference, then - if you like a fresh presentation, I would like to refer you to books such as Mahamudra Tantra by Geshe Kelsang Gyatso. If you like it more traditional, then probably Je Tsongkhapa's Stages of the Path of Secret Mantra would be a good read.
Best wishes,
SB