I strongly disagree. No way that the RATs would near-sweep the South without a Southerner atop the ticket, even if it was Scoop-Carter or Scoop-Askew. (Which reminds me, (I forgot to list FL among the Carter states that Ford would have won against Scoop Jackson.) And without Minnesotan Walter Mondale on the RAT ticket, Ford would have carried WI (which he barely lost; that was the state that would have put Ford over the top against Carter, since he needed OH and one more) and maybe even MN (two states, BTW, in which many dovish Democrats would have stayed home had Scoop Jackson led the ticket).
I agree, Carter did way better in the South than any non-Southern democrat would have. This was especially evident in 1980 when the South was very close even though Reagan took every Southern state but GA (and WV).
But I don’t see why Scoop Jackson wouldn’t have appealed to people more in enough other states (like Ca and my IL) than the hayseed Carter, even if he lost a few peaceniks votes to apathy or McCarthy. I expect it would have been another close race.