Definitely fair to question Turner.
I think they saw it like this. 3B was a huge gaping hole and there weren't many options out there other than Chapman. I don't think they fully trusted IKF so they thought they could throw spaghetti at the wall with IKF, a DH/3B who could play there for ~40 games, Biggio who had somewhat of a bounceback year and then the AAA guys like Barger and Orelvis.
IKF is the real deal so it turns out it would have been better to sign a DH/LF like Pham. Especially since he's so cheap. And Turner was signed just a couple of weeks before everyone had realized that the market had cratered and every FA left was scrambling to sign anything.
Turner is playing a lot better than his numbers suggest though. He won't beat Pham on a WAR per dollar basis, of course, but he might end the season with better numbers than him. Their xwOBA is nearly identical right now.