“During the same shiur, Rabbi Schachter said whom to marry, whom to vote for and what line of parnassa a person should choose are all halachic shailos within the purview of Daas Torah that a Posek is deputized to issue binding halachic rulings for a person to follow.”
If he did say that, it is important to realize that that doesn’t mean that a person has an obligation to ask in the first place. Also, Gedolim don’t normally issue psakim in these matters (besides voting), and would probably only do so in very specific cases.