Yukine right now are worthless. The author portrayed him as an angsty brat, now what?
You can't expecting a brat like that to improve in few weeks just because the plot demands it so. It's puberty, it's gonna took few years for him to be mature.
The author try to play it close to real life mentality, yet Yukine will have a shonen plot improvement at the end of this arc, else Hiyori will died (because she stucked in spirit form until the arc is over), and the series become dragged too long just because the plot are about waiting a puberty teenager for being mature