I actually have a different understanding of the Jōdo Shinshū teachings of Bombu (deluded being) and the concept of Tariki (power other than self), as I was just telling someone else recently. I'm not sure where in the presentation this is getting confused - whether locally, or a misinterpretation of the texts, but the teachings of one's Bombu nature are not to be taken as an apriori belief. You should not be trying to convince yourself that you are a Bombu and that you are powerless. The concept of Mappō (Dharma-ending age) is also not an apriori belief. The idea of Bombu is to take a hard, honest look at the motivations behind your thoughts, words, and actions to see whether or not those motivations are tainted by greed & anger. Interestingly, I've heard of Zen people coming to this same conclusion after years of practice. The idea behind Mappō is to take a serious inventory of one's capacities for practice and see if they are any where near those sages of old, to see where one's karma has led up to this point and if it's such that it's conducive for practice. Realizing that your motivations are tainted and your capacities for practice are limited, the next step logically, is to realize that embracing tainted motivations will never make one free of taints. Rather, embracing tainted self-power (Jiriki) will reify the tainted self. At this point, knowing the self to be tainted, you rely on "power other than self" (Tariki). This is in line with Zen master Dogen's words in the Genjokoan: "To study the Way is to study the Self. To study the Self is to forget the self. To forget the self is to be enlightened by all things of the universe. To be enlightened by all things of the universe is to cast off the body and mind of the self as well as those of others. Even the traces of enlightenment are wiped out, and life with traceless enlightenment goes on forever and ever." Aside from this brutal self-evaluation to root out one's motivations and the reliance on power-other-than-self, Jōdo Shinshū followers engage in deep listening (to see the workings of great compassion in one's life) and cultivate feelings of gratitude for the supporting causes & conditions in one's life. However, Jōdo Shinshū does not refer to these activities as "practice", as the work has already been done (again, echoes of the doctrines of other schools such as "practice of no practice" or "practice without grasping", and the Tendai doctrine of Original Enlightenment).
If, however, you come to the opposite conclusion that your motivations are pure and your capacities for practice are great, then following another path is proscribed. While Jōdo Shinshū exclusively embraces Tariki (power-other-than-self), it's cousin Jōdo Shū (more closely aligned with Jōdo Shinshū's founder's teacher) is a bit more of a balance between Tariki and Jiriki (self-power). In fact, almost all forms of Buddhism use a balance between the two (in Zen, the faith is in the practice or in Big Mind, according to Zen Mind, Beginner's Mind).
Since we're talking Nichiren Shōshū, as opposed to Nichiren Shū, I think it's important to point out Nichiren Shōshū's concept of their founder Nichiren. To quote the wiki article, "Nichiren Shōshū teaches that Nichiren Daishōnin is the True Buddha and that his Dharma, or Mystic Law (Myōhō: mystic in the sense of profound, sublime, or unfathomable), is the True Buddha's ultimate teaching. Nichiren Shōshū's belief of Nichiren Daishōnin being the True Buddha is its reason for referring to him as Nichiren Daishōnin ("Great Sage Nichiren")." This particular doctrine is no less removed from Tendai praxis than solely relying on power-other-than-self (Tariki). Also, Nichiren Shōshū is not strictly self-power, but a balance of self-power (gyōriki - lit. practice-power) and faith-power (shinriki). The faith aspect comes in the power of the Buddha (butsuriki) and the power of the Dharma (Law) inherent in the Gohonzon (hōriki).