It would help a lot to be able to build an arcade expression using the FeatureSetByRelationshipName or FeatureSetByRelationshipClass to reference a value in a separate table. The Join View option doesn't work well because if I want to make a schema change in the parent layer, I have to delete the join and then recreate it after the change, which creates a new feature service and causes me to recreate any layers and repair any maps I used that join in. The expression would run on the fly without having to create a separate layer.
