the safety is a bar of steel that physically prevents the trigger from moving far enough to lose sear contact with the hammer.. the only way the hammer can drop on a safetied AR is if one or both sears sheer off, the trigger pin sheer off, the safety bar on the trigger breaks off, or if the safety itself is removed (i doubt even a cracked safety, so long as it's still in place, would allow enough movement).
i've done quite a bit of trigger experimentation. i've made some of the most beautifully smooth, short, crisp triggers you could imagine, without reducing spring tension (and therefor not reducing strike reliability)... but the point of diminishing return is an EXTREMELY fine line. in drop testing, i had FCGs that would drop the hammer from a 6" fall to the buttstock. but NONE would ever drop hammer when on safe.

