B'fanei Nichtav in Bavel

The gemara in Gittin on 6a brings a statement from Rav Huna that ever since Rav came to Bavel, Bavel was treated like Eretz Yisrael in terms of Gittin. This means that just like in E.Y. one need not say B'fanei Nichtav, so too in Bavel there is no such need. Rashi explains that the gemara means to say that ever since Rav came to Bavel and established a Yeshiva in Sura, Bavel was treated like E.Y. as far as this halacha of B'fanei Nichtav.

Tosafos asks a strong question on Rashi. The next line in the gemara asks on this statement of Rav Huna from the mishna which implies that there is B'fanei nichtav in Bavel. What kind of question is this? Rav came after the mishna! According to the way that Rashi learns the gemara everything changed once Rav came to Bavel. Thus, according to Rashi the hemshech of the gemara makes no sense. I have my own suggestion for an answer to this question but I'll save it. For now, I'll let you give it some thought.