+1 for this. While relevance is indeed subjective to some extent, there are some clear rules which should work for everyone (else search engines like google would have no reason to be). A number of elements can be already considered in the note structure (such as title levels) and content (occurrence count, results position) to already provide an initial ranking likely to prove more effective than simple alphabetical ranking.
Furthermore adjusting the current odd default search settings seems necessary to me. Searching for “it” for example will bring up position as a result simply given position contains it. While there are some rare cases in which matching that way can be useful, it is usually not useful and simply clutter the search results (it could always be included, but then should be addressed as a less good match as if the exact term are found).
Searching through a vault is getting more critical as time goes and our vaults grow, and this is the last part of the software preventing this tool from going from excellent to exceptional!
(as a +1 including the ability to also include search query matches found in images in the search results similarly to Onenote would also further improve search)