Wing loading is simply weight divided by surface area of the wing. My question remains, has average or typical wing loading changed since the time of your teratorn, and if not, why not?
The estimated wing loading of the Argentavis magnificens is 11.5 Kg/M2. That Wing Load figure is consistent with modern birds that fly by continued flapping of their wings... a mode of flight that is not used by large raptors.
It is not consistent with the similar proportioned California Condors. The Wing loading of the Gymnogyps californian is only 7.21Kg/M2 of wing area... and they have trouble getting off the ground.
The slightly smaller Albatross, a gliding rather than a soaring bird (has a narrower wing), has a wing loading of 9Kg/M2. It has even more problems with getting off the ground and landing... that's why they earned the name "Gooney Bird."
Using your 11.5 Kg/M2 figure, the Teratorn's wing loading is almost 60% greater than wing load of the largest soaring birds today. Using formula developed by Theodore von Kármán for determining the wing loading of soaring birds, it's 19 Kg/M2 - 167%. I think that's a bit extreme... and might be because "Soaring Birds" include smaller birds such as song birds. I suspect the actual wing load figure is probably closer to the 11.5 Kg/M than to the von Kármán's. In addition, working backwards using von Kármán's formula from the calculated wing load, you find it fits a wing of only 4M2 rather than the known 6.7M2 wing area of the A. Magnificens.
If the Teratorn were adapted to modern 1G conditions, either the wing size should be ~50% larger in area or the bird needs to weigh 33% less to bring it into the range of similar soaring birds today... around 7 to 8 Kg/M2... rather than the 11.5Kg/M2 that it is.
Which brings us back to the basic problem... we KNOW the mass and we know the wing size and they don't fit.