A dead character means that:
1. they can't dps
2. someone else can't dps while they revive them
So a dead lann (or anyone else) takes away more than just their own dps. Whether this is worth it depends on the players and stats. If you're going to die, die right before the boss dies lol.
My main is a (staff) Evie and I have a Fiona who just started doing Colhen raids. I'm also level 3x on Lann. The way i feel the skill floor/ceilings will go for me:
Skill floor (easy to learn), low to high: staff evie, sword lann, sword fiona, spear lann, hammer fiona, scythe evie (I just can't figure out scythe)
Skill ceiling (easy to master), low to high: sword fiona, staff evie, sword lann, hammer fiona, spear lann, scythe evie.
This is just how it works for me, i think it varies a lot person to person.