"In the 727, if there was a commotion in the cabin, or in cargo ops a strange noise or thump or bang coming from the back it was very reassuring to turn around and ask the FE to "Go back there and see what's going on".
Can't do that on a 2 crew A/C..."
Why not?
You can go to the toilet, you can go and heat the food, you can go and "stretch your legs", you can take a 40 minute nap in your seat.
But you can't ask your F/O go back and check out a strange noise?
Of course you can! It should even be the first thing you do.