Interaction between weapon % mods and damage calculation

Idk if the title is accurate enough, but it gets the point.

In PoE 2 rn the only valuable stats on crossbows for example is x% phys dmg increase and flat phys dmg. So im wondering, if my attack converts 80% of phys dmg into lightning i wonder what use there is for flat elemental / % elemental. every ability i`ve seen for ranger/mercenary just converts phys atk and nothing of the elemental dmg on the weapon itself, even if its the respective elemental type the phys gets converted into.

My problem with this is, that on the base level everything else but %phys and flat phys is a brick (except for atk speed, but even without a t6-8 %phys mod its a brick... its basicly just the cherry on top)

I have crafted at least 200-250 crossbows to date and have never rolled a decent one. Thats so discouraging.