I've been playing a lot of Staff Evie recently and I've consistently dealt more damage than the Lanns in my party. The only exceptions are when we are fighting a very low level boss (such as a daily) where a Lann can continuously attack and where a Lann is higher level than me.
Compared to any Evie, Fiona, or Karok, Lann just doesn't have the utility that gives him survivability and more openings to attack. Even though Lann probably has the highest raw damage of all the characters, he's not insanely strong enough to make up for his lacking. A Fiona who has less damage has way more openings to attack as well as higher survivability.
I mean really, my first Titan run was with 6 Lanns (didn't think it would be so hard). It took us 40 minutes because every time a person was revived, two more would die. The sole Fiona and I (Staff Evie) lived the longest and were able to do the most damage. The result statistics really shocked me, as it told me I had dealt 30% of the damage out of a party of eight. After that experience I cringe a little bit every time a Lann joins my raid party :\.