What you consider as Gurani is Hawrami. Actual Gurani is part of the same tongue as what is ignorantly called "Kurdish proper". Its because some scholar made a mistake and confusion.

Simply because Gurani, Sorani and Kurmanji as well as Farvi-Khuri and Semnan-Biyabanaki have kept some "Avestanisms" which distinguishes them from any other Western Iranic language even from Hawrami (which you unknowingly call "Gurani"). These tongues also all are linguistically very close to the point where Farvi-Xori and Biyabanaki are as much within "Kurdish" as Gurani and Kurmanji" are). Any further linguistic shift came after that. This is not my own bias, this is clearly evident. Furthermore these tongues are called terms derived from "Gathabara" meaning Hymnbearer which are the hymns, the Avesta, that the early people Zoroastrian people brought to Iran. Note that no other linguistic groups calls itself a derivative of Gathabara and has that meaning of "hymnic" as an endonym for theit tongue. Its basically the people that were with the Magi, the priestly tribe/clan, which were the only ones to "bear the Avestan hymns" and which were said by classical Greco-Roman authors to have been taught by Zoroaster. Not only that, the king that supported Zoroaster was said to be "a very ancient king of Medes" by Greco-Romans all while the Medes are the only that have a tribe among them (Arizanti from Arya Zantu "Aryan tribe") that fits to the way the Avestans viewed themselves (which is literally an "Aryan tribe") which alluded to that group of Avestans that came to Media and settled (which the Magi were part of).

Languages change, but the continuity is given. This Avestan origin only is true for Gurani, Sorani, Kurmanji, Farvi-Xori and Biyabanaki. Not for Gilaki, persian or tatic, etc..

There is a tribe among the Guran who do have the origin history of being the people entrusted the Avestan songs by Zoroaster himself and they are called "Zand" which literally means "exegesis" even back in Avestan (Zainti-). They have this story while having been surrounded and in contact by muslims ans muslim dynasties in a muslim world. All others would make up origins from muslim rulers. Not they, for obviously it wasnt made up but perfectly fits to them being called Zand and being Guran (Gathabara) and speaking the tongue that shares most linguistic features with Avestan from any Iranic tongue plus being from the people that the Magi were from (Medes).

You can look at historic accounts and try to find the Avestans in Central Asia, but you wont find them, only Scythian groups. Thats because there was a Climate catastrophy on the steppe and at that very time the Scythian nomads would spread and replace people. Fast forward you have the hereditary priest group and people that Zoroaster taught in a region where the people literally call themselves "Gathabara" and are linguistically the closest exactly from a time onward where Iranic presence in Media and especially Kurdish regions on the Zagrus rises very high (in Assyrian and Babylonian sources) and where they also bear actual Zoroastrian-derived names (Bagafarna) and terms (assara mazash = Ahura Mazda).

Pretty obvious if you ask me.