It is too much work to use Seraph effectively. To get really high damage from her she needs to be at low health (not my game-style) and/or attack marked enemy. Since she consumes the mark, you have to reapply it every round. Honestly I just prefer Arb, HM or BH, especially against very high HP enemies. She has a guard, but without prot or dodge buff, so it is not good against enemies like Vvulf, Prophet or for dodge teams. Her stun causes horror, so you should bring laudenum or you use her guard afterwards. She can be a mark boot, but it is a luxury just includes her for this purpose. I tried to use her but now I just don't bother with it.

I have the same problem with the Lamia. Since I use my healers (even Vestal, she can be an excellent stunner with her CC trinket set) rather offensively, her human form doesn't fit to my play style. I don't like when every fight is practically 3 against 4, especially because her heal/stress heal is not that high. If I transform her for every other battle, I have to somehow handle both the shuffling and more importantly the stress. I also practically have given up her.

It is pity because they are great mod classes with good lore, trinkets etc. At least I frequently use the Sisters, Thrall, Wraith and sometimes even the Falconer.