And you have to be realistic too. Rodriguez has over 100 big league innings under his belt. He might not be proven relative to Roger Clemens or Randy Johnson - but he's a big leaguer with the tools to be a hell of a lot more. He is going to be part of the 2016 rotation, and he's a sophomore. Owens is where the more interesting question lies, and I do see your point, and certainly the team needs 7 or so guys they can turn to for the reasons you cite.
Now if they go to the market to get a Cueto (just to put a name out there), then you are looking at a pool of starters with Cueto, Buchholz, Rodriguez, Porcello, Owens, Johnson, Wright, Miley, which is less daunting. One of the areas the brass screwed up in 2015 was not just the rotation that started the season, but not churning aggressively. Of course when the team turned into the 2013 Mariners for an entire month, the churn probably would not have helped much unless you could deliver the 1971 Orioles from behind the curtain.