Don't forget, not every Molle vest is a Plate Carrier. You can have the versatility of a Plate Carrier with a strict Molle Vest, without the weight of adding armor, and/or the restriction of a looser fit due to lack of armor in it.
When talking airsoft, even the heavy weave of a Molle adds a fair bit of stop power to the bb's, compared to an assault/tac vest, which is basically 4 straps with pouches sewn on. Having said that, you can get a load carrying Tac vest, with Alice type attachments, for a similar effect to that of a non PC molle.
I have both, btw, Tac and Molle PC, with IV plate. When you've run with 100lbs on your back, on top of your gear like a bitch, you don't sweat the dif between molle and tac much. Unless the PC is fitted with IV plate, or even just IIIa soft. But for the sake of this thread, Stay light. Stay quiet. Stay alert, stay alive.
If youre the point man on entry, wear as much armor as you can. However, If your in the thick, a bit of plate isn't going to save you past the first few hits in a heavy fire fight. Sooner or later you'll catch one outside of the boiler room, that's still in a lethal zone. (inside thigh, under arm, neck etc.....) Better to be mobile, because no matter how much plate you strap on your chest and back, you aint a tank dude.