Aside from the cam being wrong, there is a "tolerance stack up" that should be considered. Quality Control has specs it lives within or, plus or minus so much. Your crank snout keyway is plus or minus, your lower sprocket key way is plus or minus, the sprockets themselves are plus or minus and the cam is plus or minus.
It doesnt take long to see that you'd have to be one lucky S.O.B. to have the cam timing come out perfect without checking and adjusting.