Not sure I agree. After WW1 Forest spent 18 of their next 51 seasons in the top flight. After promotion in 1977 they won the league in their first season back and spent 16 years in the top flight. Only twice in those 16 years did they finish outside the top half, with 7 finishes in the top 5. In the 28 seasons since Clough stepped down, 4 have been in the top division.
Since WW1 Forest have had 38 seasons in the top flight, 57 in the 2nd tier and 5 in the third.