I didn't mean to imply they were mutually exclusive; just that in terms of "most high-impact documentation you can write", I find ensuring I link the ticket higher than making sure I have a thoughtful commit message, for the reasons listed.
Fair that it can disappear eventually if you change ticket trackers or whatever; that's a risk of changing ticket trackers. Hopefully you maintain both for a bit, and once you're six months out or whatever and retire the old, you don't need as much context since things have moved on (and there's a generational effect in tickets akin to that in garbage collection; you tend to need recent things more often than old things, and the older, the less likely you are to need it).
But just in terms of "what would I rather have", a link to the ticket every time. And in terms of "what am I more likely to provide", a link to the ticket every time as well (since all the communication on the ticket came about out of need; writing a thorough commit message is out of preparation, and I, and everyone else, am WAY better at consistently doing things that I need to do than preparing for possible future things)