According to the last possibility you cited for your question in Insights to the Daf on Taanis 17a, if they hold it's not a real Gzeira Shava, why would the Gemara say it and why does nobody else give that same answer?
>>(d) The CHIDUSHEI HA'RAN in Sanhedrin (22b) and the KEREN ORAH here explain that the Gezeirah Shavah is not a real Gezeirah Shavah. The verse which says that Kohanim may not let their hair grow is a verse in Yechezkel. A Gezeirah Shavah from a verse in the Torah to a verse in Nevi'im is not a real Gezeirah Shavah (see Chagigah 10b). It is only a "Giluy Milsa." Therefore, Abaye asks that since it is not a real Gezeirah Shavah there is no imperative to learn anything from the laws of Nazir. Consequently, the Gemara asks that perhaps a Kohen may not grow his hair at all (literally) and he must shave his head every day.<<
Jeremy A, Brooklyn, USA
1) The Chidushei ha'Ran writes that it is only a Giluy Milsa. We can translate this as meaning "a definition." It is a way of defining the word "Pera" (???) as meaning hair that has not been cut for 30 days. In the same way that we know that a Nazir must let his hair grow for 30 days, we also know that the Kohen should not let his hair grow for more than 30 days. This form of derivation does not have the authority of a Gezeirah Shavah (such that we could say that it has the power of a Halachah given to Moshe at Sinai), but it is an accurate translation of the word "Pera" and this is why the Gemara says it.
2) It may be that some Mefarshim disagree with the Chidushei ha'Ran and the Keren Orah and maintain that sometimes it is possible to make a Gezeirah Shavah between a word in the Chumash and a word in Navi. There may be a source for this in Zevachim 59b, where the Gemara cites a Gezeirah Shavah of "Ravu'a-Ravua" about the Mizbe'ach being square. The two places where Ravu'a is stated are Parshas Terumah and the book of Yechezkel, describing the Mizbe'ach.
The Mitzpeh Eisan, at the back of the standard Gemara there, writes that this is not a Gezeirah Shavah but rather a Giluy Milsa, because we rule that one cannot learn Divrei Torah from Divrei Kabalah (words of the Nevi'im).
3) However, the Har Tzvi, on Shas there, cites the Teshuvos Har Tzvi (by Rav Tzvi Pesach Frank), Orach Chaim 1:43:5 (end of page 44b and beginning of of page 45a), who cites Zevachim 59b and writes that one cannot learn a Gezeirah Shavah unless it was received from one's teacher, but there is a difference between the words of Torah and the words of the Nevi'im. Concerning a Gezeirah Shavah from Divrei Torah, one derive it only if one's teacher received it from his teacher and this chain goes back to Moshe on Har Sinai. In contrast, a Gezeirah Shavah from Divrei Kabalah must be received from one's teacher and the chain must go back to the Navi who received the Gezeirah Shavah and wrote the verse through Ru'ach ha'Kodesh. It is said about the words of the Nevi'im (Divrei ha'Yamim I 28:19), "Everything is written, from the Hand of Hash-m, He bestowed His Seichel upon me." (See also Margoliyos ha'Yam, Sanhedrin 22b, #4, who cites a number of other examples of Gezeirah Shavah based on verses in Nach.)
Kol Tuv,
Dovid Bloom