I don't think weight is a large factor in build quaiity. Money is more important. A formula 1 or LeMans series race car weighs less than half of a typical road car and when they crash it into a wall at something around 180 mph they not only walk away from that incident, they race the same car two weeks later 🙂
Or compare a knights armor to modern body armor, a crossbow bolt penetrates a knighs armor and some plastic stops a .38 bullet.
Magnesium is good enough for race car wheels and I have never seen brass used for this.
Oops, forgot to meniton something more important than build quality, ergonomics!
Weight is a big part of that, a heavier body might be easyer to use than a lighter one.