Far as Dahlia vs. Thetis is concerned I prefer the latter--she has status immunity and well-rounded stats while Attack IV instead of Risk Life III isn't a terrible trade if you're mostly using her on rare maps where you need to UP ramp or tie up paralyzing units anyway. Dahlia mostly shines vs magic users and that's a role which faces a lot of competition from outside of the Valkyrie class. I don't really foresee myself ever using Dahila much given that I've already invested some fodder into Sybilla, Thetis, Claudia, Imelia, Horace and Conrad.