Question

Hello,
In the Talmud in the Daf Yomi, the Gemara says that it is impossible that the Torah excluded a tumtum from the commandment of appearing, because a tumtum is a case of doubt, and it is impossible that the Torah excluded a doubtful case.
I understood that it simply is not reasonable to say that the commanding authority explicitly addressed a case of doubt, but I saw in Rashi that he explained: from where would we even have thought to obligate him? Therefore, no exclusion is needed.
Now, according to the view that in a Torah-level doubt one must be stringent by Torah law, how is the Gemara's statement to be understood—that it is impossible for there to be a verse excluding a doubtful case? After all, that is how he understands all Torah-level doubts: that the Torah obligates in a situation of doubt. So what exactly is the problem with saying that the verse is speaking about a tumtum?