Jenkins is obviously one of the more talented hitters in the game, but he's just as obviously one of the gimpier hitters in the game. He's nearly 30 years old, and he's never played more than 135 games in one season. The last three seasons, he's played 105, 67, and 124 games.
What I do know is that 1) the Reds are stuck with Griffey, and 2) the Brewers were not stuck with Jenkins; they didn't have to commit $23 million to Jenkins seven months before his existing contract expires. Oh, and 3) as much as the Brewers needed to reassure their fans that yes, they really are trying to win, they may well come to regret giving Jenkins a big new contract when there were still seven months left on the old big one.