Full text search usually presumes an index, for a lot of functional differences compared to the browser's naive substring-matching Ctrl-F. And any proper search index is going to be a better user experience than naive string matches.

I haven't read through all of Lunr's docs and source, but based on my Solr/Elasticsearch experience, I'd expect to see (in time)…

Tokenization and (presumably) term normalization/analysis; a faster and smarter query language, for term order independence and boolean combinations of clauses; relevance scores and maybe even score boosting per field.

Better queryability really shouldn't be understated here. Just having term order independence focused on a specific set of JSON is going to be way better than naively matching any substring on the entire rendered page.