It is so weird how people act like this is a thing.
- No reason castillo needed to be on team, he was bad and left team out to try after signing him to a contract
- No reason the team couldn't upgrade bullpen without trading Narvaez
The reason you give up on Narvaez would be if you thought his bat was the issue, but he has now posted back to back years with a 120 wRC+. That beats our 1b, that beats our DH, and it beats the last several years of DHs. He has a high obp, his bat can handle the lower .iso - because he was cheap and under control.
A 1.5-2 WAR LH hitting player that can play catcher and is plus offensively would be valuable. The team needed a "defensive" catcher for their pitchers, they chose Castillo over Narvaez, not McCann over Narvaez.