I had thought that perhaps a specially reinforced floor might have been installed in a cargo 747, but I can see how you explanation is lighter and still fit for purpose.
The floor boards are essentially just shear panels to handle any shear loads through the fuselage. Unless you're willing to do a major redesign and a big flight test program to prove that design, the load paths must remain the same. In freighters the major components in the load path (the seat tracks and the floor beams beneath them, plus the attach structure of the floor beams to the fuselage frames) are beefed up. But all cargo loads must still react through the seat tracks, into the floor beams, and then into the primary fuselage structure. This is fundamentally different than military airlifters. (at least American, Italian, Japanese, and Russian military airlifters. I have no idea how Airbus designed the A400M and they seem to do a lot of things differently.)