I understand where you're coming from with the whole "no guarantees" argument, and Niskanen is a really good example of that. My problem is that Smith should've been up last year because he was one of our top 7 defenseman within the organization--it's the same issue I have with Tatar not being in the top 9 with Detroit. If Smith was up playing last year, that could've/should've precluded the Quincey trade (Lidstrom, White, Kronwall, Ericsson, Kindl, Smith, Stuart). As bad as Smith has been (which I still believe has ALOT to do with Babcock destroying his confidence), that's easier to handle with a steadier Lidstrom-led defense.
Also, while Smith playing with Lids and Stuey might not have guaranteed him being better for this season, it definitely wouldn't have hindered his development. It appears that leaving him in the A did just that.