You can't just divide a code base that's entangled. If you disentangle it, you'll remove some bugs in the process. My feeling is that it's super-linear for this reason.
Completely agree. And my favourite add-on is if it’s broken apart such that one half of it ends up being a library, adding a second consumer to that library will tend to further reduce bugs, even more so if the second consumer is written by a different team. (Eventually, at least, because the second consumer is going to find bugs so the start)