perhaps the larger number of ancient arrows had naturally tapered shafts - cane type shoots.
like lots of things about trad archery, tapered shafts is one of those things that's NOT a mainstay gotta-have given, just something on the periphery that might make shootin' better, easier, etc.
i diverge a bit ... best to think of trad archery first in terms of the simplistic basics - a decent bow with the best matched arrows possible that yield consistently good arrow flight, and of course your ability to slip that really sharp c-o-c broadhead into a critter's boiler room.
all the rest of the nuances (arrow type, string type, feather type shape foc, gpp, lmnop, etc and ad nauseam) aren't as important .... ymmv.