Lightning strike damage calculation question

so we know that lighting strike has 2 components to it, the melee strike, and the projectiles

so for the strike portion, its basically your weapon damage * (gem level's damage + any physical damage + strenth's physical mutliplier) then half of that gets converted into lighting, where its further increased by elemental and lighting damage right?

but what about the projectiles? they dont take that exact formula right? it'll be reduced by 30% plus any other modifiers from support gems and then also lose the strength's physical multiplier?

so getting iron grip will only improve the projectile's damage by just a fraction? is this really worth getting? or is there something im missing here?

I feel the same way played with iron grip for a few lvls wasn't impressed.