i do not know what is so difficult to understand and why u are now talking about 1 weapon being affected by 10 weaponskill instead.
here, i know better way to explain:
u have 10 uncle. all visit house for family reunion
each uncle give u $1000 pocket money, and if u playing same sports as uncle, he give 20% extra because he like u more.
at end of day, each uncle's wife, ur aunties, say 'ok, if u wearing same color clothes as my husband, whatever all ur uncles given u plus ur current savings combined together, i give % bonus based on that total sum, between 3.5% to 13%)
therefore, there no real point to measure weaponskill bonus on 1 weapon, 1000 x 1.35 = 1350 because it apply to sum. u should be calculating about total, not individual weapon.
edit: so it not misunderstood, ur math in quoted is finally correct, but focusing on wrong thing.