My hypothesis was that

Assumed Damage Calculation wrote:k*(SkillElement%)*(BaseAffinity*(1+Affinity%)+MagatamaAttack+WeaponAttack)*(1+Attack%)*(1+Element%)*(1+SkillForce%)

like I wrote in my guide. Pretty much proves that the element and skill force (and the partial elemental thing) parts are correct, although due to the small sample size (I only took 3 readings and averaged them out), it's probably not the best proof (the 500 damage deviation is likely caused by this).

Exorcist Arrow is 50% Pierce and 50% Holy, hence 27 Pierce increases its damage by 13.5%. I had no other Element / Skill Force at the start (without Magatama).

A question, what does k represent?

I wanted to do some quick testing with this to confirm (unless the wiki has something else). If this equation holds, then doesn't this mean any increase in affinity, skill force, or other would result in a linear increase in damage?

k is everything that is out of my control. Enemy defense, element, so on. Actual Skill Force is included in there as well since it's not really important here.

How does skill force work? My rapid shot V has 255 skill force while icicle storm VII has 316. But on yakumo, rapid shot deals only around 2-3k a hit while icicle deals more than 10k on the initial hit with ~3k each on the extra shard hits (non-crits). Does each hit of rapid shot and the icicle shards have a 1/3 coefficient or does the main hit of icicle have a hidden multiplier? Also, how is it calculated, is it a multiplier to your attack damage? (like a 200 force skill should deal double compared to a 100 force skill)
I'm guessing it means 100% of attack for a 100 force skill, I've done a bit of searching but I can't find anything about it.