The thing I find funny is that when Frost was hired, it certainly wasn't sold as a six year rebuild. It was gonna be a much quicker turnaround. But now that he's had a losing record 4 years in a row, now "it's a 6 year rebuild."
David Cutcliffe, when he first got to Duke, got 4 years of almost an identical record to Frost. His 5th year, he went 6-7 but made it to the Belk Bowl (first bowl game since the 90s). His 6th year, he won 10 games. That's the closest comp I can think of off hand. One huge difference in why Cutcliffe got more time despite the losing records is that Duke went 4-42 the previous 4 seasons prior to his arrival.
Cutcliffe
2008 - 4-8
2009 - 5-7
2010 - 3-9
2011 - 3-9
2012 - 6-7
Frost by comparison
2018 - 4-8
2019 - 5-7
2020 - 3-5
2021 - 3-7