How/why do attacks work differently when targeting and dont have a consistant attack speed?

Andele

When starting a attack without targeting, you can move the crosshair over a npc to hit it, and for friendly/neutral npcs with Prevent Attacking Innocents on the attack just passes through them (which is likely programmed by not acquiring them as eligible targets/ignoring npcs with certain flags for aoe/damage acquisition). Yet one cannot start a attack (and even some skills that dont do damage/aoe buffs) while the crosshair is in the vague hitbox of a target with it on. Why make a double protection of npcs when the second serves no reason but annoyance?

Also why do light and heavy attacks (especially if mixing the 2) sometimes have inconsistent attack speed/downtime/cooldown between eachother? e.g. if one holds the heavy attack on 2h for around 1.1s (between when the character starts moving the elbows faster again after the over0the-top windup and the handle/blade reaching the shoulders) and then presses light attack right after, the 2 play "irl correctly"/without the massive overswings and hit in under half a second from eachother. BUT then there is also the case against "tall enemies"/where you have to aim up and the heavy attack que sometimes bugs out, that if you wait and let go when the swing is at the shoulders, using two light attacks will cause the second one to come at a far greater delay (instead of new attack animation starting once the character grips the weapon with both hands; also 2h light attacks only use 1 hand, the irony; it will only happen once the weapon goes back to idle animation/is held vertically again).

Apologies if this is a old topic that was explained somewhere, but google doesnt want to show the results in that case (or im using the wrong keywords).