A hundred and fifty degrees separates two signs that share nothing. They are of different modality, different element and different polarity, and in the sign-based doctrine of Hellenistic astrology two such signs are not in aspect at all. They are said to be in aversion, meaning they cannot see one another. The quincunx is therefore not a weak aspect in traditional practice; it is the formal name for the absence of an aspect, and the tradition is explicit that nothing passes across it.
Modern practice inverted this. Having moved to degree-based measurement, where any angular distance can be assigned a meaning, twentieth century writers gave a hundred and fifty degrees a reading of its own: adjustment, chronic low-grade strain, a relation between two things that cannot be resolved and must instead be continually managed. The name inconjunct survives from the older usage and now sits awkwardly beside a body of interpretation that treats it very much as a conjunct thing.
Both positions are live and they are not reconcilable, because they disagree about whether the configuration exists. A practitioner working from Hellenistic principles will pass over a quincunx without comment; one working from a modern text may treat it as among the most diagnostic angles in a chart. Orbs given to it are correspondingly narrow, usually two or three degrees, which is itself an admission that the aspect is being asserted rather than inherited. Anyone reading a chart that turns on a quincunx should know which of these two traditions the reading is standing in.