When congestion is sustained and QoS has already been optimized, the correct design response is to add capacity rather than continue tuning packet treatment. QoS manages contention by prioritizing, queuing, shaping, or dropping traffic, but it does not create additional bandwidth. If access-to-distribution uplinks are persistently oversubscribed, business applications will still suffer because the offered load exceeds the available link capacity. Implementing higher-speed uplink interfaces increases the physical bandwidth available for aggregate traffic. Bundling additional uplinks into EtherChannels also increases usable capacity and improves resiliency while presenting a single logical link to the switching and routing design. Random early detection and selective packet discard can improve queue behavior under congestion, but the question states that QoS is already optimized and no longer effective. Reconfiguring QoS to IntServ would add complexity and is not a realistic campus fix. Therefore, the architect should increase uplink capacity through faster links and EtherChannel where the hardware and cabling support it. Reference topics: campus oversubscription, EtherChannel, uplink capacity planning, QoS limitations, congestion remediation.