Firstly; thanks for taking the time to report this issue - we really appreciate it. It's sparked a rather interesting discussion on the build team - so thank you for that.
Unfortunately, we've marked it as a "won't fix". We believe this issue is caused by a bundle generated from a newer version of Unity being used with an older Unity runtime. We appreciate we could improve the UX around this, but it's unfortunately not something we're able to do for any of the current Unity LTSs given that they've also been bumped to support the latest AssetBundle format.
We've created a ticket to be more mindful of this in any future AssetBundle updates to ensure that it doesn't happen again.
Thanks again for your time.