I don't know about the "git log should stand on its own". Chances are that when you finally migrate to another ticketing system and the ticket numbers in your commits "break" or become meaningless, you do not care much about that old history anyway.

And even if someone is interested in an old commit that contains a ticket number for a ticketing system that does not exist anymore, the commit itself (the code changes, not the message) tell the story as well, just not in prose.