I consider that a local problem that only you have. None of the several person using TB daily for more than a decade have encountered this kind of performance issue.

What have you tried to find the cause of your performance issue ? Have you tried making a new user profile to test if your local profile got somehow corrupted ?

Yes, I've tried many things, including a new profile. Compacting would help for a few days. Thunderbird just doesn't seem to do well with large mail archives going back more than a decade. That is my experience and the experience of others.

Also, I've met many people who experience similar performance issues, so I find it bothersome that because you've never encountered it you're asserting it does not exist.

This is also an issue that's span multiple machines and multiple clean installs.

Add me to your new list then. TB starts up in ~1min. Sometimes it will just hang for a few minutes while updating emails/calendar. (Can't switch to its window) Sometimes it will take 10s+ to dismiss a meeting reminder. Sometimes the meeting reminder can't be dismissed. Sometimes it will get confused by filters working slowly and both beep for a new message and then immediately move it away.

There are bugs upstream for all of those. They're up there for years.