Ranged. why you gotta hate???
Any bow user is going to end up wanting or using pinion or be miles behind in dps.
which means nearly every one of them is likely to use the planar conflux set.
since red dragonscale seeker 10 is already replicated on pinion, and ranged bow users have to do whatever they can to stay relevant, the go-to-option seems to be black dragonscale armor
by making the (pitifully small) ranged damage bonus aspect of the black dragon armor set an artifact bonus that does not stack with planar conflux, since every ranged build worth anything is using a pinion and planar conflux, this is POINTLESS and makes the items valueless, or at least worth a lot less
fixing it to a different set bonus would also be pointless because, so far, the only black dragon helm I have seen has +3 insightful dex. Dex is an important stat for most ranged builds, which is why MOST of them try to get treads of falling shadow, which covers all their non-exceptional+1 dex needs. so the helm would be redundant or force them to find +8 dex elsewhere where it may not be as practical.
PLEASE, for the already-barely-relevant-in-endgame archers out here, do this:
make the set bonus from the black dragonscale armor stack with the planar focus set, or remove the ranged component of it entirely and give some other ranged bonus
let there be an as yet undiscovereed version of the black dragon helm with +3 str , con or wis on it, not only dex.