Jorm's real value is in the atk down debuff summon effect. So, it sucks that you missed Jorm...
...which is why you should make sure to be around for Yatagarasu's event! Yatagarasu also applies -10% atk on summon, but on a 9 turn cooldown. It's an advent type event about... 6 events away or so.
(the DMM order after Rahab is: Crom Cruach*->Ixion->Quetzalcoatl->Apocalypse/Phoenix reprint->Yggdrasil->Pride (first Union type event!)->Yatagarasu)
*old Irish deity; I only figured out who the eidolon was supposed to be by copy/pasting the katakana from dmm wiki to ja.wikipedia.org)
Jorm is indeed quite good, but is replaceable by Yatagarasu, a fire eido with atk down coming 2 months later.
More importantly, you still can max out the first 3 advent eidos from their revival, which are the most valuable ones.