My 12 accounts are spread over a handful of providers, with emails going back to 2006 in some; While I agree thunderbird's search is inferior to gmail's, its global indexer is decent in capabilities and horrible in ux, whereas the "standard" search is horrible in capabilities and speed, but decent in ux.

I use the "expression search" addon, which is perfect as long as you only need to search on metadata; and the global indexer when I do. It's not perfect, but it doesn't make me want to quit in anger, and not even to surrender my privacy to google.