This isn't true. That is the kind of power loss you might see if the automatic tranny was a hydraulic pump driving a hydraulic motor. It's not, of course. Just like with a manual tranny in direct, all the gears inside are locked together and it's a straight shot in the front and out the back. A small amount of power is used to pressurize the forward and high clutches to lock the plantes together--but we're talking 100psi here. The converter is the thing that in the past sucked up power--but maybe a 3% slip cruising. It's slipping is what increases torque but that only happens when it is loaded. But since the 80s torque converters don't slip past about 35mph because they are also clutched now when not needed. These days, there's not much difference in manuals and autos mileage wise. In some cases, autos can post better mileage even.
I don't know why people think manuals are old school and autos are modern. Autos have been around since about 1940 in cars. I mean, after 70 years of being able to drop the stick in D and press on the gas we should be getting ready for the next thing--like CVT.
Incidentally, after flipping through the Serivce Manuals on my wife's Honda Pilot I saw what I thought was a manual transmission blow-up. Turns out, the Honda auto uses the same type of gear arrangement as a manual-shift tranny and not planetaries.