Zimmer had the reins of what was arguably the best Red Sox team of all time, the 1978 team. In a way he was incredibly unlucky that season turned out the way it did. But he had a hand in it by burying Lee that year, among other things.
You can drive yourself batty with woulda shoulda couldas. They're pointless.
The way I look at is, since Henry bought the team the moves have mostly been great, and the mistakes have all been surmountable.