I read the book of one of Carter's campaign strategists and what she says is that Carter was ahead, largely due to the very fractious GOP primary. Kennedy then started to make life difficult for him. The surge after the DNC was due to Carter getting Kennedy out of the way and Kennedy endorsing him. Reagan also got the surge for similar reasons.
The 1980 GOP Primary was less contested than either 1976 or 2008.
The only thing we can actually see, and discuss are the public polls, either now or in 1980. Those showed it close, but as late as a fortnight before the election Carter was leading by 3 and was at 45%.
Some of the tracking polls did show a sharp shift.
Your own linked article does not back you up. Of more than a dozen polls two weeks out, the single Gallup one is the only one to have Carter ahead. In fact, Gallup did another pre-debate poll with Carter down in the chart provided by the article.
Reagan would have been leading the RCP average by about 5% heading into the debates if it had existed then.
