Nowadays we are being asked to accept illegal aliens as the functional equivalent of citizens, and they are strongly pushing this "citizen of the world" bullsh*t.
If you control the narrative long enough, you eventually control history.
In 1800, Virginia was the number one population state and half of Americans lived in the South.
So there's no reason to think Southerners in 1800 had fewer printing presses than Northerners.
By 1820 when the term "is" was used about 1/3 of the time, Virginia had fallen to 3rd most populous (behind NY & PA) and the South to roughly 45% of all Americans.
Still there's no reason to think Southerners had fewer printing presses than Northerners or that the "era of good feelings" was felt less by Southerners than other regions.
Sure, by 1860 the North & west were beginning to run away with population numbers, but the "era of good feelings" was past and only 20% of usage went to "is" versus 80% to "are".
Who exactly in 1860 were the "isers" and who the "arers", we don't know, but we do know "isers" increased steadily until around 1900 they made it official & permanent.
Yes, nobody disputes that the last famous holdouts for "are" were Democrats, but they were Northern Democrats, your alleged "Northeastern Power Brokers" heavily dependent on Solid Democrat South votes.
Point is: it's not all "North vs South", but rather various sometimes shifting alliances which since at least 1836 have included Northern Big City Democrats with Southern Democrats.