Gratitude for Shakyamuni Buddha specifically and people generally is necessary for the subjugation of ego vital for awakening.

I disagree with all the scholars assertions regarding original and acquired Enlightenment and my arguments transcend even the discrepancies found in Nichiren's A, B, and C works*.

"A" works are those in Nichiren's hand or known to have been in Nichiren's hand. "B" works are those works not in Nichiren's hand and never known to be in Nichiren's hand but for the most part, agree with those works in Nichiren's hand. "C" works are those works not in Nichiren's hand and are for various reasons known to be forged or apocryphal writings.

https://jstone.mycpanel2.princeton.edu/wp-content/uploads/2015/09/Review-of-Hanano-J%C5%ABd%C5%8Ds-Tendai-honkgaku-shis%C5%8D-to-Nichiren-ky%C5%8Dgaku-2011.pdf

We can come to understand not only how Nichiren taught and believed Medieval Tendai Original Enlightenment but his teachings on acquired Enlightenment (receiving and keeping).

If we look to the Five Major Writings and the entire authenticated canon of Nichiren we can correctly come to understand Nichiren's works with the caveat that Nichiren's thought evolved over time. Certainly, Medieval Tendai Original Enlightenment was believed and taught in Nichiren's earlier works, predominantly those before ~1261/1262. After, around this time, Nichiren more forcefully taught the concept of receiving the seeds of Enlightenment from the Original Buddha and watering the seeds through the chanting of Namu myoho renge kyo.   

The evolution of Nichiren's thought is that specifically, Shakyamuni of the Juryo Chapter is the Original Eternal Buddha and generally, we too are original (or ancient) Three Bodied Tathagatas in our own right. Nichiren teaches however, "if you confuse the general with the specific, even in the slightest, you will fail to attain Buddhahood." An understanding of these concepts can be gained through the paradox of "one but not one and two but not two."

Some, particularly the Soka Gakkai, mis-teach the principle of the equality of the Buddha and the common mortal because they misunderstand the principle of the general and the specific. They sometimes teach that the common mortal is equal to the Buddha and sometimes that the common mortal is superior (that we are the original teachers of Shakyamuni Buddha). It is different when the Buddha proclaims that the common mortal is equal to the Buddha, since this is a Buddhist paradox. Understanding [living] the paradox with gratitude for Shakyamuni Buddha is a necessary part of the subjugation of ego vital for awakening. Nichiren scolded the Zenmen for the same transgressions exhibited by many Nichiren sects (that the common mortal is the original Buddha and teacher of Shakyamuni Buddha). I can support my view with the authenticated writings of Nichiren, the Lotus Sutra, and even the questionable writings utilizing the Buddhist paradox of "one but not one and two but not two". They who mis-teach the equality of the Buddha and the common mortal or the superiority of the common mortal to the Buddha can not. In fact, without gratitude for Shakyamuni Buddha specifically and people generally, there is no Buddhahood.