Are service disconnects (one large amp breaker in a panel) considered main panels or is the next panel downstream considered the main?
The equipment with the first disconnect is the “service equipment”. It might be a panel or a disconnect. If it’s a panel I call it a service panel. If there are multiples e.g., 2x200 amp panels (none downstream of the other) I call all of them service panels.
Panels that are not service equipment, I refer to as “distribution panels”.
This eliminates confusion about bonding jumpers. Service equipment gets the grounded bus bonded to the equipment ground. Non-service equipment does not.