San Francisco 49ers : biggest year-to-year improvement/decline

Based on regular season win percentage:

                            Change in 
                              win %
Improvement: 2018 -> 2019     0.563   (0.250 -> 0.813)
Decline:     1998 -> 1999    -0.500   (0.750 -> 0.250)
Last Year:   2024 -> 2025     0.353   (0.353 -> 0.706)