A method and system to control carrier aggregation in a wireless communication system including a first access node and a second access node, where the first access node has a first respective backhaul connection, where the second access node has a second respective backhaul connection, where the first access node supports serving user equipment devices (UEs) with standalone connectivity, and where the first and second access nodes cooperatively support serving UEs with dual connectivity. A method includes detecting that the second respective backhaul connection of the second access node is threshold heavily loaded. And the method includes, based at least in part on the detecting that the second respective backhaul connection of the second access node is threshold heavily loaded, causing the first access node to suppress an extent of carrier-aggregation service that the first access node will provide to any standalone-connected UEs, to help free up capacity for dual-connectivity service.