Relentless Refactoring is a great tool, but one that is often stymied by faddish behaviors like micro-services/modules. Small projects tend not to have that problem and so make a better petri dish. Of course then you have to take your knowledge out of the 'lab' and apply it in vivo...
A lot of our (and in particular, my) best features come from of relocating the boundaries between things, to make space for features that weren't considered in the original design. With monolithic systems we see this late in the lifecycle in the form of Conway's Law. If you stick this problem in front of the CI/CD mirror, it's painful to face. CI/CD argues that if something is difficult we should do it all the time so that it's routine (or stop doing it entirely).
However there's a conspicuous lack of tools and techniques to make that practical. The only one I really know of is service retirement (replace 2-3 services with 2 new, refactored services), and we don't have static analysis tools that can tell us deterministically when we can remove an API. We have to do it empirically, which is fundamentally on par with println debugging.