The only issue with "large" mailboxes is that Thunderbird tends to become really slow. But this issue plagues other desktop clients as well.

I would love to find an actually performant email client. It shouldn't take like seconds to sort like 100 000 emails. It's a puny number. The time it takes one can read all the emails from disk a thousand times, it's sad.

Hate to admit but Apple Mail is the only one I know that has fast (albeit simple) local search even for large mailboxes.

On Mac I’ve found MailMate to be excellent in this regard.