How do you adjudicate a dispute where a colleague block...

The colleague is likely misinterpreting a controlled deletion study as a definitive architecture comparison. A well-trained single-vector retriever, such as ANCE, can reach high performance by optimizing negative sampling. To resolve the dispute, you should measure the actual Recall@k of your first-stage retrieval at the depth you can afford. If the bi-encoder achieves comparable recall to the multi-vector index, the 5.7x storage cost of the multi-vector approach provides no practical benefit.