The Rambam writes that Shabbos is dechuya in a situation of pikuach nefesh. The Kesef Mishna says that his source is from tu'mah where we pasken it is dechuya and not hutra. The Maharatz Chiyus asks from our gemara. How does the kesef mishna assume that since tu'mah is only dechuya, therefore shabbos is also only dechuya? Our gemara makes an assumption that shabbos is hutra for the korban tamid, yet tu'mah is only dechuya. We see from here that although tu'mah is only dechuya, shabbos can be hutra, so how does the kesef mishna make the assumption that they should be the same?
In my opinion the kesef mishna is correct. The issue is not a shabbos vs. tu'mah issue, rather the reason our gemara assumes that shabbos is hutra for korban tamid is because the mitzvah of korban tamid is meant to be done on shabbos. The system was set up with the natural conflict and the resolution being to bring the korban tamid even on shabbos, therefore rendering it hutra. However, when the two events conflict by chance or by circumstance, then it is dechuya, not hutra. Therefore, tu'mah b'tzibur is only d'chuya. Shabbos in the place of pikuach nefesh is also only dechuya because it is just circumstances of someone being in a life threatening situation that creates the conflict. Therefore, it is legitimate to learn shabbos for pikuach nefesh from tu'mah, and not learn from shabbos for korban tamid.