Explanation:
Cisco native YANG models provide the most complete and current support for Cisco-specific features. IETF models are standards-based and suitable for simpler or early automation use cases. OpenConfig models provide vendor-neutral consistency and are commonly used for larger, more complex automation deployments.

Multichassis EtherChannel is the correct design when distribution switches support VSS and the campus needs fast Layer 2 convergence while using as much uplink bandwidth as possible. With VSS, two physical distribution switches operate as a single logical switching system from the perspective of the access layer.
MEC allows an access switch to bundle links to both distribution chassis into one logical EtherChannel. This removes the normal spanning-tree blocking of redundant uplinks, uses both links actively, and provides fast convergence if one physical link or chassis fails. A plain EtherChannel normally terminates on one physical switch, so it does not provide the same chassis-level resiliency unless the distribution pair is virtualized. RSTP improves loop convergence but still blocks redundant Layer 2 paths in a traditional topology. ECMP requires Layer 3 routing, and the question notes routing protocol limitations. Therefore, MEC on VSS is the best solution for bandwidth utilization and fast Layer 2 recovery. Reference topics: VSS, Multichassis EtherChannel, Layer 2 campus resiliency, STP avoidance, access-to-distribution design.

Section: Advanced Enterprise Campus Networks