Every situation is different. I have no intention of increasing the number of cows I run, so I want the cows I have to wean more pounds. That doesn't mean monster cows. People seem to forget that there are two sides to a ledger, expense AND income. People also seem to think that it's a choice between monster cows and little cows. Raise a style of cow you like and continue to demand more from them. Maybe I'm greedy, but I want moderate cows (moderate might be subjective and vary by habitat / locale ) that stay in the herd and wean heavy calves in 210 days.
I don't buy feed, but I have a real good idea what it costs me to make it. The difference between feeding a 1350 lb cow and a 1100lb cow might be $50 on the real high side if you believe small cows always eat less than a larger counterpart. If she gives me 200lbs more calf then that feed was a great investment.
In the summer time my cows are on grazing tenure that is a around $3.20 per AUM. Doesn't matter the size of cow. If I had a third more little cows I'd pay that many more AUM's. I'd also have a vet bill 1/3 higher, 1/3 more selling expenses, etc.
I think if those selling the 1000 lb cow idea really believed the numbers they'd switch to sheep or lowline cattle.