I am confused by the logic. If the pen let Monty down (turned a lead into a deficit), then he would receive a no-decision, not a loss. The only exception would be if the pen let enough of his inherited runners score to flip the lead.
Rather than guess about this, I took a quick scan of his game log. Monty lost nine games with the Cards in 2023. There is a common thread, but it isn’t the relievers.
In seven of those nine full games (not just while he was pitching), the offense scored three or fewer runs. Six times, they scored two or fewer runs. The Cardinals were shut out in three of his April losses, starting the season on the wrong foot. Only once when the offense gave him more than four runs of support in 2023 did he lose.
In his nine losses, the offense scored an average of 2.56 runs during the entire game.
So the data tells me that it was the lack of offense, not the pen (or the rest of the rotation or the defense), that contributed most to Monty’s losses.