One feature will not dictate an increase/decrease in subs. No one can draw a correlation specific to RDF.
I do think other changes, in addition to RDF, that caused the watering down of realm/guild social experiences eventually made retail into an unsatisfying game.
This is why some of us fight against RDF… not because the tool, by itself, causes the demise of the game but to curtail any tool that places QoL over realm communities/social experiences.