Yes it is... but the loading is more consistent with birds that flap their wings to maintain flight... not with the birds that share body morphology with the Teratorn... the soaring birds.
Now put an engine on that wing... one that can keep it flying. One of the other scientific papers I linked on this discussion reported that the energy necessary to keep the Argentavis flying as a soarer, not even as a flapper, was about 600 Watts - but the Teratorn was only capable of producing 130 Watts - and that calculation was based on using a wing loading similar to a modern Condor of about 7 Kg/M2 not the 11.5Kg/M2.
As for not flapping for take off, there is a technical term for birds who have to wait for wind to take off... Lunch.
I’m going to ask again: there are many extinct bird species; do you have any evidence that average or typical wing loading has changed since the age of the dinosaurs? Have you even bothered to consider the question? If not, why not?
I have considered it... and the evidence is that the morphology of the Teratorn is essentially identical with a modern Condor... but scaled up without the necessary physiological changes in musculature and skeleton to support the additional weight.
By the way, the Argentavis magnificens lived and flew and died to extinction a little over six million years ago... nowhere near the time of the dinosaurs. But there is evidence that gravity may have been even more attenuated when dinosaurs roamed the earth...
Take, for example, the Hatzegopteryx thambema, the largest known species of Pterosaur with a wing span that reached 12 - 15 meters (40 - 50 feet). It's skull was nine meters long... Estimated mass was 400 - 500Kg. (880 - 1100 Lbs) with a wing load of 9.1 Kg/M2.
Artist's representation of Hatzegopteryx thambema
It was larger than the Quetzalcoatlus Northropi, with its 8 - 10 meter wingspan, whose mounted skeleton is pictured here:
Quetzalcoatlus Northropi
Any problems getting airborne the Argentavis magnificens would have these creatures would have ... in spades.