A ship of Theseus is fine as long as, at any given time, you have a seaworthy ship. MacOS deprecated 32 bit applications just a few years ago, that's a chunk of dead wood that got stripped out, some people are sticking with the older OS so we're in a transition period on that right now.

A series of small incremental steps is vastly superior to a complete rewrite, or massive re-engineering project from the ground up every 10 years.