In my mind, spine is the most important ingredient. However, straighting is also critical because the shaft will not fly consistently if it is crooked or warped and not straight. Matched arrows require close weight tolerances. Of course, if the nock [e.g. relative to direction of grain] or point [e.g. too much weight] are not attached correctly, the shaft will not fly straight. Fletching may or may not be less of a problem but can still significantly affect arrow flight. Each of these can impact arrow flight -- depending on how severe the issue is -- the greater the flight deviation.
I guess that with all of these potential variations and considerations producing a finely tuned and matched set of wooden arrows is a challenge.
Just my thoughts! Tox Collector