The 747 has just one boom. What’s more important than the amount of fuel it can haul is how many booms are available for aircraft needing to refuel. That’s one reason why the USAF is buying the KC-46A based on the 767 rather than the KC-45 based on the A330.
I did find the picture of a test flight with the 747 tanker refueling an SR-71 to be interesting. That’s one use of a 747 tanker that might be justified for performance reasons. The 747 is the fastest subsonic jetliner. The SR-71 had to slow down to almost its stall speed in order to refuel with a KC-135.
LOL, I know...I was making more of a 747 lover statement! Why should the dang Iranians get one and not us????????