That's sort of all wrong.

Old testing has all separate buffs stacking multiplicatively, because SE is cool like that.

Does need to be confirmed though.

That said, even if similar buffs are additive, IR should obviously still be used with the others because a higher chance to crit on attacks that have a 20% damage buff is good. The only buffs that you could possibly argue "don't need to be stacked" are BFB and Raging Strikes, which is still incorrect since you want both of them to synergize with IR/Barrage/Hawkeye, even if those two don't synergize with each other. Net result is that you're still using them all at the same time when feasible.

The only note is that you do not want to hold any buff for later for the sheer purpose of stacking them.