Manoah was a legitimately very good starting pitcher in his first 1.5 seasons. He may not have been a true top of the rotation ace type but he was absolutely still a good top of the rotation pitcher, just more realistically a good number 2 starter. The ERA numbers, particularly were very unlikely to be recreated as the FIP/xERA numbers trailed by a full run, but even after this correction he was still a great contributor to the rotation.
His 2022 3.30 xERA result placed him 16th in MLB among qualified starters, the 3.35 FIP placed him 19th, the 2.23 BB/9 placed him 24th etc. The stuff numbers suggested some level of correction to the results moving forward as he's never really featured anything other than average stuff across the board, and as more of a pitch to contact type who relied on inducing soft contact there was also the possibility that the shift ban was going to further compound his issues against left handed hitters. Having said that I just don't think there is anything analytically that would have suggested the complete implosion that Alek suffered in 2023.