Table 2 and 3 tell you basically all you need to know. When you use a harness that is tuned towards programing (Codex and Claude Code), grep wins. When you use a neutral harness, vector search wins.
So far every Grep vs RAG discussion I've seen conflates overlapping factors. The most common is simply that a company rebuilt their pipeline from scratch and fixed a bunch of problems. The worst is when they go from one-shot RAG to multi-step Grep and completely miss the fact that multi-step RAG would likely get them similar results.
At the end of the day, the most important thing is knowing the _product features_ your users care about and making sure that's represented in the pipeline.
If you install LSP. AFAIR their first versions used some kind of treee/structure for easy search, but they found out that grep was better/similar but with less complications (they now ship some kind of grep).
So far every Grep vs RAG discussion I've seen conflates overlapping factors. The most common is simply that a company rebuilt their pipeline from scratch and fixed a bunch of problems. The worst is when they go from one-shot RAG to multi-step Grep and completely miss the fact that multi-step RAG would likely get them similar results.
At the end of the day, the most important thing is knowing the _product features_ your users care about and making sure that's represented in the pipeline.