With a .459 winning percentage, the 2023 Mets are tracking to 74 wins. Versus the 101 last year, this would easily be the biggest season-to season drop-off.
The next closest:
1976 to 1977: -22 wins
2008 to 2009: -19 wins
2016 to 2017: -17 wins
Still in play is the record for greatest swing (in either direction).