In golf shafts, the variation of spine isn't important as the club is only gripped in one direction, whereas a pool cue, you never know what rotation you have. Golf shafts though, are all spine matched before the grips are installed so that the flex is always the same. It was the same for early arrow carbon fiber shafts also. We always spine tested them before fletching them to have a consistent fletch. Did it with wood, did it with aluminum, and did it with carbon.
As to pool shafts, not sure there is enough of a difference to matter with the current gen of shafts as you are seeing them made both ways, and as you mentioned, even the flag wrapped ones are mostly chris crossed layers to get around this.