I think injuries are the most common reason why players - even young players - have slumps. I also think staying healthy is one of the most important skills a player can have. If one player has a slump because he is out of it mentally (also a skill) or because of random variation instead of an injury, it's still the same result. Lets say Cabrera's slumps were due to injuries as you say (and you are probably right). That doesn't make him any better than another hitter who slumps for other reasons. It's still a bad overall performance. The sum of his skills at the end of his career were not helping the team.
As for Ibanez facing a RHP, Cabrera was hurt as often as Ibanez faced a RHP the last few years!