Don't forget the context. The only starters on the team when they traded for Chavez were Stroman, Dickey & Hutch. They had Sanchez - but nobody knew what he'd be able to give the team as a starter (and most expected him to struggle mightily). Estrada and Happ had not been signed yet (nor had Floyd).
This team needed starting pitching depth BADLY. Could they have waited and seen whether they were going to get Happ/Estrada/Floyd? Maybe. Maybe not. Hard to know, but it's not hard to see a scenario where this team needed Chavez in the rotation a lot this year (injuries, Sanchez struggles, Happ signs elsewhere, etc.). It never materialized, but that doesn't mean they were wrong for adding the SPing depth.
In all likelihood, we probably would have been a better team this year with Chavez in the rotation and Dickey/Thole sitting in Margaritaville.