A base station that is configured to provide first-RAT service on multiple carriers will reserve at least one of the carriers for use in providing UEs with dual-connectivity service on the first RAT and a second RAT, and the base station will reserve at least one other of the carriers for use in providing UEs with standalone first-RAT service. For instance, a 4G base station that is configured to provide 4G service on multiple 4G carriers could reserve at least one of those 4G carriers for use in providing UEs with EN-DC service (where each UE would be served concurrently on a 5G carrier as well) and could reserve another one of those 4G carriers for use in providing UEs with standalone 4G service.