Final Fantasy XIV Database - Ffxivpro.com

It's probably already been said before but simply put:

Although almost all marksmanship weapon skills are 30% AGI based, however, STR is factored into all physically contacting weapon skills and directly calculates against mob VIT and defenses thus usually having a much higher overall benefit compared to secondary modifiers.

The only time secondary modifiers heavily stacked will really stick out is if the mob is nailed with dia 3, Angon and an acid bolt with attack food and double minuet or chaos roll active on you, assuming you have a good handful of STR to begin with. This of course also depends on how heavily mod dependent the WS is to begin with of course. Anything below oh, I'd say 40% shouldn't over prioritized against STR in my opinion unless you meet those previously mentioned conditions.

Long story short: STR directly calculates, secondary mods add slight base dmg. Detonator due to it's higher base accuracy is good to go mod heavy, while slug shot in of itself does quadruple damage but tends to whiff, so go with lotsa r.acc.

Hope this helps~

Side note: R.atk is God. It's very difficult to grasp in gear and is in very selective foods, but the results are incredible.