I'm all for shaking out the roster as the season progresses. Good teams need to cull the weak and bolster the lineup, rotation, bullpen, etc.
But why bother starting the season with guys you are 90% certain will be terrible? I guess it's okay if you're willing to gamble on that 10% chance they'll succeed and capture that old magic, or that they'll get off to a hot start.
Unfortunately, when that gamble pays off, teams tend to ride that bet way, way too long. Danny Graves piling up 30 Saves by the All-Star Break in 2004 convinced a lot of people that he could "get the job done." That worked out well, didn't it?
Make yourself a better team as the season goes on, but don't start the marathon by running backwards.