I don’t know much about guns but I did a bit of poking around once. IIRC, the AR-10 is much different than the AR-15. In particular, it is much heavier. This is the very fist thing that I noticed in comparing the two side by side. For me, the immediate implication was that what would be really nice is to have one of each. The lighter weapon is good for closer quarters (ahem) target shooting, while the heavier weapon is better for longer range (ahem) target shooting. In particular, an AR-15 is good for toting around in the field, but an AR-10 will get heavy very quickly when one is traveling longer distances on foot, especially with other gear plus (heavier) ammo.
Ideally, one would have two each in case of a jam.
What would be interesting is a cost breakdown of the machining tools that are needed— particularly the milling machine options.
I am dimly aware that the AR-10 can shoot .308— is that correct?
They do not have to be heavy, thought the Armalite products usually are. The new DMPS models have a couple that are barely heavier than the AR-15, and lighter than some.
Of course, ammo is always heavier, and when you add a scope to take advantage of a longer range round....