That's a really good point and I think it's not yet clear how well, say, 8-30MB worth of regexs with accompanying algorithmic structure would do on these tasks. I would imagine they do quite well on a well defined task, but it would be much harder to then adapt this set to a new domain. A big part of Needle's promise is how easy it is to finetune. Ultimately I think the two approaches can be more complimentary to each other, rather than choosing only one (see triggers!).

I think a good "traditional" approach would look like a BM25 algorithm over an index of trigger phrases for each category, sitting behind a majority-vote classifier. The "fine tuning" would be done by reindexing the data, generating different/new phrases, and tuning the classification threshold.