I like the focus on traffic shape. I would add one more comparison layer: cost per accepted outcome, not only cost per model call.

For RAG or agent workflows, a cheaper model can still need more context, retries, reranking, or eval passes. That can make raw dollars-per-million-tokens misleading.

The budget I would want to see is workflow-level: input, output, retrieval/context assembly, fallback/retry, and eval/judge calls.