It’s unfair to characterize my comment as a solution - as the reply responded to in an edit it’s not really a problem. The redirect renders changes to the slug effectively meaningless.
Freezing slugs assumes the original title and resultant human-readable portion of the URL is in some way superior to the renamed version. If that’s really the case why would you want your users to be able to rename topics at all? That was my contention.
Assuming for a moment that topic renames are beneficial, why wouldn’t you want the human readable URL to receive the same enhancement?