We have the M240L which is a lighter shorterbarrled version.I keep forgetting about that.
Actually, the weight is due to the M240's mission profile and powder load requirements. If I remember right, to have lengthy bursts or continuous fire with 7.62NATO you'll need something that can take the heat and pressure, and it is only recently that we've improved metallurgy enough that being light, maintaining that capability, being durable enough to take the pressure, and keeping it cheap(ish) isn't mutually exclusive anymore.
And I honestly like the GD Design, the mussleis a little weird, but I am a fan of bullpups