N souls are pretty useful.

[Halteclere]

I noticed that N souls have more stars in their skills' power rating than their higher rarity class ups. To add to that, their skills also cost way less MP to cast, so are much more spammable as well. I did a little testing, and by the looks of it an N soul can deal more damage per point of SP than an R soul by virtue of having more skill casts at their disposal.

I have a Departed Soul equipped with the crystal shop armor and it 1-2 shots everything other than bosses so far with its AOE skill (I'm at Finamar shrine). I teamed it up with a Burglar for the speed party boost and a Light element Cook for healing and a speed buff, and it can generally clear battles before the enemy can pull off a single attack. It's a good way to fast forward to the dungeons where you can start farming Quorite.