I read an article from a Boston sportswriter on trading Swihart for nobody. He had mangled an ankle, but the manager did not give Swihart consistent starts at catcher. Apparently a great athlete when Boston drafted him: could play several positions, good hitter, had pitched with 98 mph fastball, but preferred catching.
This article (Boston Globe?)
https://www.boston.com/sports/boston-red-sox/2019/04/17/blake-swihart-top-prospect-released/
yes, I think the team mismanaged his development. I don't know if they were thinking that he could be like a Jim Leyritz and catch as well as backup positions. The pitchers loved throwing to Leon, and Vazquez was always going to be a premium defensive catcher. More or less, they would no trade a bit of D for what looked like a better offensive skill set. Then Vazquez started to hit, so that was the end of it. Right now, their backup is Plawecki, who you know.