yes, it is applied in combat, i.e. it is an "invisible" stat. You can still see it if you click on blue "skill" button on the kamihime portraits: it will show all weapon skills that will apply to said kamihime in battle
- - - Updated - - -
Medusa is Dark, In future for atk/hp we will only get thunder, fire and wind eidolons (we will get plenty of each element, just not atk/hp)
Next Gacha update will bring us Raphael (SSR light), that is probably one of the worst SSR hime in game (if we get her in "post rework" state, then she's ok at best) Uranus (SR light), that is pretty good for light team, and Inanna, (R light), that is "meh", but who cares about R-tier anyways?