WRT researching relationship quality, I would probably start by asking how I can tell a high-quality relationship apart from a low-quality relationship, then by going out in the world and seeing what kinds of relationship structures correlate with relationship quality.

The trouble here is that different relationship types serve different goals. You're more likely to come up with a flowchart which takes you from values to recommended relationship type than the claim that relationship type X is better for everyone than all other relationship types.