Straightness, spine and weight are all important characteristics of arrow shafts. I've bought .003 straightness carbon shafts for a long time, and while spine and weight might be close within a particular dozen shafts, some that I buy a year later might be enough different in spine and weight to matter, especially when they get mixed in with the ones I bought a year before as replacements. I would rather be shooting .006 straightness shafts that are all within close tolerances of weight and spine than .003 straightness shafts that are not within the same close tolerance of weight and spine.
OTOH, Howard Hill was famous for going through onlookers at his exhibitions, borrowing arrows from different people, and hitting targets with these mismatched arrows. I think it's a stretch to think that if we start shooting mismatched arrows, we can learn to shoot like Howard Hill, however. 🤪