This depends on your users and doc corpus. On finance docs and with users that use jargon and acronyms heavily, BM25 can fail on trivial queries... you end up encoding a masters in economics into the query re-writing logic.

Double hard if you're dealing with private market finance customers with their own ideas on what "common" terms mean. I tried to replace the embedding/ingestion pipeline multiple times and nothing I tried was better over a large amount of documents. Performance sucked, the agent was re-writing and re-trying queries over and over until it found what it wanted, and vector search with a little work up front was worlds better (though it was expensive)