It doesn't mean that Imamat cannot be through the Zalim zurriyat (It is primarily through the Zurriya of the Prohpet). It says, that from THIS zurriyat, whatever it maybe, the Zalims will not become Imams. So,
Abu Bakr = Zalim = Not Imam
Nizar = Zalim = Not Imam.
When Imam Mustansir AS was alive he had appointed Nizar as the Imam openly. When he died the brother-in-law of Musteali and a female relative claimed that Imam had changed the Imamat from Nizar to Musteali on his deathbed. Then Musteali imprisoned Nizar and his son. He had Nizar killed and his son escaped. However, soon Musteali was killed and Amir became Imam, etc. Finally tayeb and he went in occultation.
Big question is that the Sura you quote says that Imams will not be in line of the Zaalims. So Tayeb's line disappeared from the face of the earth and Nizar's line is still running? Any explanation here?
Also, one of the Fatimid Dai's, Syedna Al-Kirmani says in his Islamic Treatise on the Necessity of the Imamate, please see it under the heading, which I posted in the Bohoras and Reform says;
Ismail's Imamate was valid because he produced offspring who continued the imamate; it is essential aspect of their authenticity that a descendant of his peform in the present the required functions of the office. If there were no imam now, there could not have been one in the past; if the duties of the imam are not currently fulfilled by a properly designated descendant, the ancestor CANNOT HAVE BEEN THE IMAM.
"Aside from the philosophical component, al-Kirmani upheld a range of Shi'i doctrines, particularly as interepreted by the Ismailis. For him the the imamate was a living institution with a visible. imam. It was of paramount importance in religion and all aspects of life that required the constant attention of its supreme leader. The imam was (and is) the repository of knowledge and truth.
Now the Dai's two nieces verified the scripts and agreed whatever was written in the scripts were true translations.
Albeit, he was referring to the Ithanasheri Imams here but later on it came to be true for the Tayebis too, don't you think so? Can you or your Dai prove Kirmani wrong?
One more question, why does not the Dai, if he thinks his dawat and his Imam are true, then why not open the manuscripts in his possession to the whole world. Why was he trying to grab the manuscripts from Hamdani, Poonawalla, and Zaid Ali? Was he afraid truth will come out.
He still has a chance to prove his dawat and his Imams true by opening up his proofs to the Harvard University which has introduced ISMAILI HISTORY as a subject. It was only introduced recently.