I believe it's impossible to determine the number of games a manager is responsible for winning or losing based on any objective data. Therefore it's a subjective judgement based on unproveable observations.
For many years posters on Twins Daily have pointed out numerous times (correctly in my opinion) Rocco has made poor decisions in the following areas of management:
. line up construction
. pinch hitting (especially righty / lefty substitutions)
. situational offense calls (bunting, stealing, hit and runs, etc.)
. starting pitchers being left in too long or pulled too quick
. relief pitching utilization
In my opinion, baseball (pitching and hitting) is the most precise and difficult thing to consistantly do well for extended periods of time in all of human sporting activities.
Wins and losses are not a great judge of a manager because the performance of individual players win and lose games. A great manager is someone who blends the use of statisically analysis with how players are currently performing and a gut feel of the game to make the best decisions. All players being fallible humans have strenghts and weakness, and hot / cold streaks. A great manager puts players in situations where they are more likely to succeed then to fail.
After many years of observation I don't Rocco has what it takes to get the most out of his players or put them in the best positons to succeed. In other words, I rate him as a below average manager that I iwould replace if I owned the team and was trying to win as much as possible given the resources (players) available.