SPARTAN-420:
I'm an avid airsoft player, myself, and... Well, you're not *entirely* correct about the armor. Most of us use armor in some fashion. My gear is mainly to protect my core when I maneuver through dangerous terrain. Though most of our protection is in the form of either moulded Kydex plates with foam fill, or woven Kevlar with a backing of COrdura or ballistic Nylon.
Most of this armor is designed in such a way as to conveniently carry and protect your ammunition, sidearm, tertiary weapons and explosives, specialized equipment, hydration and communication gear for convenient use during combat, as well.
And properly designed and fitted armor doesn't impede movement much more than simply its weight.
THAT BEING SAID.
There's a difference between a 6094 platecarrier in Kevlar and Cordura and knee pads, and a homemade sci-fi armor suit.