Well , i found out this , with full osiris gears, your damage will be : skill description x 20 ( output may varied depend on your honing but not so much) . And if you refine your gear, just x40% on the damage xD ( per 10 refine min/max = 1% additionnal damage).
I am not sure, if I understand you correctly. The damage equals only by chance x20 your skill decription. It's due to the simple fact that yor PSE might be 2000 at that moment and the result might also depend on the defense rate of the target.
Refining your gear doesn't improve the weapon damage by a given percentage, but it's the same for all classes. It doesn't matter if you refine a level 10 weapon or an Osiris weapon... a +1 refinement will always give you +4 damage.
The priest however can also refine the Bible to get an additional MATK bonus. Like I already stated, MATK is just weapond damage in disguise, so if you divide the value by 10, you can evaluate the additional damage increase (before skills). And there are still other ways to increase your damage: F.e. power seedrunes, Osiris cards, etc..
Sadly most of these values aren't shown in your character screen.