> They told over and over again that customers didn't care about search quality, they just wanted to see a list of 350+ data sources that the product could index.
This seems to describe corporate buyers ticking boxes on a form, more than actual users.
(1) Performance. Back in the day people frequently turned full text indexing on Windows off because it would slow down their computer too much. People won't be happy with the overheard of a search engine that is always scanning 10's of GBs of document.
(2) Search quality. People are familiar with Google being an effective search engine but they've certainly tried a number with terrible relevance scoring and probably learnt that it is not worth trying the search on a web site or the search on the help of an application. In the case of Elasticsearch the default similarity is BM25 but that has two tunable parameters. There are other similarities you could use but most of them have tunable parameters. It makes a real difference what you choice and there is a methodology for tuning them that is now built into ElasticSearch.
https://www.elastic.co/guide/en/elasticsearch/reference/curr...
I talked to about 20 vendors of full text search products and found that only 2 out of the list regularly evaluated the quality of the results, 1 of them just did it so they could get some advertising by being on the TREC leaderboard. They told over and over again that customers didn't care about search quality, they just wanted to see a list of 350+ data sources that the product could index.