Spectrum aggregation has been a key enabler of LTE and 5G capacity growth and will remain essential in 6G as networks combine fragmented spectrum across low bands, existing mid bands, new upper-mid/centimetric bands, and millimeter wave bands. This article examines how 5G carrier aggregation (CA) and dual connectivity (DC) inform the design of 6G spectrum aggregation. The central thesis is that CA is the necessary carrier-level scaling mechanism, while DC is a higher-layer cell-group architecture that should be used only when a second cell group is genuinely needed. We argue that CA provides a cleaner and more scalable foundation for multi-band operation in standalone 6G. Building on lessons from 5G, we advocate enhanced CA as the preferred 6G spectrum aggregation framework and point out the corresponding key enhancement directions.

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