Why is that person “pseudo” Da’as Torah, vs. an expert on the subject matter?
Which person?
???? ????? ?????? ????? doesn’t give capabilities to someone who doesn’t have them. If not, we would be discussing Nevuah, not Da’as Torah. All ???? ????? ?????? ????? means is that the Sanhedrin is law, no matter the qualifications, not that Yiftach, Rava, or Rabbi Amital is a Navi (or has Ruach HaKodesh, or Da’as Torah, or other capabilities) like Shmuel was.
If daas Torah means extending what you ask a talmid chochom into areas beyond Torah, then the same way, despite not having a R’ Akiva Eiger or R’ Moshe Feinstein today, we still find someone who is a talmid chochom to ask our shailas in Torah to, we would also find a talmid chochom to ask our non Torah shailas.