The Jays, just like any other team will have a whole list of players in which they regret giving up, and will have a whole list of players that they got for a song.
Unless there's an alternate universe where Chavez is pitching shutouts for the Jays, there's no way to know if he'd be any good here. Maybe Oakland had a coach that managed to get through to him, just like Bautista found the right mix here which he didn't find in his half dozen other organizations prior to that.