> A "correctly layered" app with UI view separate from UI logic separate from server-side logic etc. will show up as coupling, if commits are feature oriented.
It would show some coupling commits, but e.g. bug fixes should/would be segregated to the relevant files, not spread across the system.
Basically bugfixes would be localized to relevant files, but features would spread across files.
The grandparent's making an important point in that you can't design a system such that all possible changes you might want to make are localized to one area of the code. Engineering is about trade-offs: if you rigorously separate view from logic from database, you make it harder to add features that must touch all three. Conversely, if you make each feature its own file and add in hooks to the view/logic/database layer so they call out to plugins, you make it easy to add new features but very difficult to understand what each layer as a whole is doing.
The best you can do is choose the ideal architecture for your particular project, in the particular point in time that you're working on it. That's why basically every software system needs to be rewritten as it grows up: the ratio of complete rewrites to new features to bugfixes to maintenance refactorings changes as the system matures and the requirements become more precisely known. It's also why we have a software industry; if there was one ideal way to design a system for all domains and all points in time, someone would go design it and be done with it, and none of us would have jobs.
For context, I'm talking about the initial phase of a product's lifecycle, where you are changing the product definition roughly every couple days, the total codebase fits in one person's head, and you spend much more time writing code than reading it.
Systems like PHP + "SELECT * FROM database_table" or the MEAN stack, where you use the same data format for both backend storage and UI and intermingle logic with templates, are significantly faster for getting something workable on the screen that users can try out. I've done a complete MVP in 4 days with PHP; a roughly equivalent app in Django (which has some minimal model/view/database separation) took about 2-3 weeks. The fastest I could launch a feature in Google Search that touched both UI and indexing was roughly 6 months; as you'd expect, that has a very rigorous separation of front and back-ends.
Now, the PHP solution will quickly become unmaintainable - with the aforementioned 4 day project, I no longer wanted to touch the code after about 3 weeks. But this doesn't matter - it's 10 years later and the software is still serving users, and I long since moved on to bigger and better things. And that's my general point: what's "good" code is context-sensitive. Everybody wants to work on nicely-factored code where you can understand everything, but there is no business to pay you unless you first make something that people want, and oftentimes that takes hundreds of iterations (including many fresh starts where you throw everything away and rebuild from scratch) that are invisible to anyone collecting a paycheck.
It would show some coupling commits, but e.g. bug fixes should/would be segregated to the relevant files, not spread across the system.