Da’as Torah is not that Gedolim can’t make a mistake, that is just silly, let alone Kefirah.
Da’as Torah is that the more one attaches themselves to Torah, the more their decisions become based on the Torah and not outside factors.
For example, Rav Moshe when saying IVF is Muttar brought in “Da’as Torah”. He felt that others that were saying that IVF is Assur were not speaking from Torah values, but their own personal biases (even though they may have been Tamidei Chachomim as well). Rav Moshe was saying that the Halacha that he paskened was only based on Torah and not external factors like such biases.