There are many good reasons for having nested vaults which have nothing to do with speed or number of notes, and, as I explained, the system doesn’t imply a silo.
I agree that if they were only used because of speed problems they would be a workaround, as would separate search engines if that was the only reason for using them, but I also said that if this situation ever eventuated that there would be a plugin with indexed search.
Yes, Google was a faster engine than Alta Vista, Excite, Yahoo, Bing etc al. All were indexed, all had databases. What do you think happened to programs that had integrated Alta Vista into their core?