Why Thunderbird is inadequate for opening a 7-gigabyte mbox

I opened my mailbox in Thunderbird.

• importing the mailbox is a pain
• had to create a dummy account first
• takes a number of minutes to open the mailbox
• uses 800-950MB of VM and 400+MB of RPRVT memory to open the mailbox
• sorts by default by date message claims to be sent, although there seem to be anomalies; this clusters spam
• uses 7-9 minutes of CPU to render a threaded view, during which time the UI is unresponsive; when you sort by something else and re-enable the threaded view, it takes another 7-9 minutes
• is there a way to hide the junk messages?
• I marked a bunch of messages as spam and a bunch of other messages as read in order to train the junk filter. Then I (actually Beatrice) selected all messages with interesting-feature-A (which took less than a minute of CPU time, during which the UI was unresponsive) and selected "Run Junk Mail Controls on Folder" from the Tools menu. This marked a number of the messages I'd marked as read, but not as spam, as spam. There is no obvious way to distinguish the messages that I have marked as spam and the messages Thunderbird has marked as spam.
• on the plus side, Thunderbird doesn't seem to want to store its updates to message status flags as Status: headers in the messages.
• on the minus side, it seems to be storing that information in a 176MB Mork file, which could make it hard to get it into anything else.
• Despite the fact that Thunderbird isn't storing which-message-is-read information in Status: headers, it seems to believe Status: headers added by spammers.
• Thunderbird thinks I have about 500 000 messages in this mailbox. But I actually have about 800 000.
• Scrollbars are not useful on a 500 000-item list.