If you watched the Chargers' games, you would know that their WRs could not stretch the field at all. They were a dink and dunk team and their YPA was one of the worst in the league, despite having a top five QB. Their receivers stink and there is no way they don't take either Kincaid or a WR in the first round. With Herbert, they have the ability to outscore the Chiefs, but not with their current crop of receivers.
Branch is a very good player, but that would be an unwise use of a first round pick.