User blog comment:Nicholas0524/Darvenshel or Oulu?/@comment-25251916-20141029011017

The JP video could be an old video. Darvanshel's batch wasn't released immediately after Trial 3 was introduced. I think it was a month until his batch came and it started becoming easier with Darvanshel due to the reason that he can do damage while offering damage mitigation. Darvanshel as a leader is a possibility but there is also other potent leaders that can be used such as the coveted Lilly Matah + Grah combo.

Maybe another reasoning behind the Oulu is that the summoner might not have had RNG by their side to summon a Darvanshel and had to stick with the Oulu. There is also the fact that Oulu might have been the only damage mitigation unit they had at that certain time.

Ushi, a popular BF youtuber, released a vid where he had Darvanshel as his leader and a different healer besids Altri. Here is the video below.
 * https://www.youtube.com/watch?v=lEvO4OaAVwI&list=PLcMZD3lNa9k0r6rNhM77rRSCk30Qwu9Cz

I prefer having Darvanshel over Oulu considering Daru can impact the fight more with a more solid way to BB regen. Tech Gizmo 2 is alright for Darvanshel but Evil Shard works better because it allows him to passively fill it up. Generally the best combo sphere for him is Dandgelga + Evil Shard, which allows 5 BC generated per turn and has the nifty increase of 30% HP and ATK. Evil Shard can be obtained as an Arena reward or by Frontier Hunter HR 15.