I’m in the ‘depends’ camp too. (And purposely chose a PPO over a managed care plan for that reason alone.)
If a medical issue pops up for something (ankle/knee) that relates specifically to someone we already have a relationship (ortho), we’ll call their office directly. Ditto Derm or ophthalmology or gastro or even general surgery. When we complete the patient questionnaire, we always list our primary care doc’s name so he’ll receive a report.
OTOH, if it’s something for which we don’t have a relationships with a specialist, we’ll call the primary care doc. Basic blood work is reviewed by primary care doc.