I'll start by pointing out that hindsight is 20-20. Particularly among position players, things usually even out in the course of a full year. Baldelli started the season with Donaldson injured in the first inning and a bunch of experienced position players not hitting including Garver, Sanó, Polanco and Kepler, as well as Cave, who due to injuries got a lot of playing time in the crucial first six weeks. Rocco stuck with all of them, which makes sense. Some guys came out of it, a couple namely Kepler and Cave, did not. Simmons was so anemic on offense, that his very good defense was negated by being a black hole at the bottom of the order. On the pitching side, Columé was dreadful, but guys like Duffey, Alcala and Thielbar weren't getting crucial outs. All four of those guys came out of it to a degree, although Columé was barely passable all season as a bullpen arm. In the rotation, Happ and Shoemaker started April with better than acceptable numbers, but both were beyond bad after their first few starts. The expected starting pitcher depth didn't develop as planned--Dobnak got knocked around and was injured, Duran wasn't great in AAA and got injured, Balazavic was injured immediately and inconsistent at Double A and so starts were given to Ober (success!) Barnes, Jax and Albers, none of whom were expected to contribute this year or maybe ever. Canterino, Winder and Enlow were all injured along with the aforementioned Duran so the high ceiling guys did not move up the ladder as anticipated. I think those things were largely out of Baldelli's control. Add in injuries to Buxton, who missed 100 games, and Garver, who missed more than 50, and it can be understood that maybe they wouldn't win the division or make the playoffs.
I didn't like some of Rocco's decisions, but he had a roster with no real backup shortstop and bench players who are bat-first and mostly slow. As far as pitching decisions go, I would have liked to see the starters challenged to pitch a sixth or seventh inning more often, but I understand the concern that there isn't much in the tank after facing 18-20 hitters with max-effort fastballs and breaking balls and the possibility of injury does go up at some point.
If I am grading the manager, I'd give him a C, which is average. I think the front office deserves a worse mark in providing talent for the major league team.