The Eagles took 5 years to rebuild from their SB winning 2017 team to their current NFC best 2022 team. Five years, not 2-3.
Denver has been rebuilding since 2015, with only one winning season in there (2016).
Seattle was last good in 2020. Last year they went 7-10. This year, in year 2 of the rebuild, they're 6-5, with Geno Smith as their QB, who is not the long-term answer.
The Dolphins won 10 games in 2016, then have been building ever since, with only one good year since then (10-6 in 2020). They are finally really good, but it took them a long time to get there, not 2-3 years.
The Bengals won 12 games in 2015 and had their first good season with Burrow/Chase/Higgins/Mixon in 2021, a stretch of 6 seasons.
The Panthers have been rebuilding since 2017, when they won 11 games. No more than 7 wins in any season since.
The Falcons were last good in 2017 as well, when they won 10 games. Since then, they haven't won more than 7 in any year.
The Steelers won 12 games two seasons ago in 2020, but since then they won 9 and now are 4-7. Their rebuild looks like it will take more than 2-3 years since they're already in year 2 and they suck.
I could go on but you get the point. The idea that rebuilds back to contender status only take 2-3 years in this day and age is absurd and demonstrably false.