various quirks and derailments of LaunchServices have already been plentifully discussed here and elsewhere… I have recently excluded my external backup drive from Spotlight search and all seems to be well in „Open with…“ (so far).
One question I still have though to which I couldn’t find an answer yet:
I can rebuild LaunchServices (via Terminal scripts) as often as I like, restart Finder, reboot the computer, etc. - the date and the innards of com.apple.launchservices.secure.plist remain unchanged. The folder in which it lives (~ /Library/Preferences/com.apple.LaunchServices/) updates its date/time stamp every time I rebuild LaunchServices but not the .plist file itself.
(iMac late 2013, 16 GB RAM, El Capitan 10.11.6)