Levinbolt seems pretty lackluster to me. Maybe I'm wrong, but after picking this up at level 30, it still seems much better to me to go with Radiance / Damnation over Radiance / Levinbolt.
Levinbolt is nice if only for the reason that you can get sp for both the Levinbolt attack and the Manabolt status effect. Not to mention that Manabolt actually appears to do decent DoT as well.
Since you should rarely be running into MP issues at higher levels anyway, the chance for extra sp is more useful.
Radiance You gain 150 conjury skill points.
VS.
Levinbolt You gain 150 conjury skill points. Manabolt You gain 75 conjury skill points.