However, it helps tremendously for imperfect code to exist in a disciplined higher-level organization. In particular for OOP, this means interface and package/assembly responsibilities should be clearly-defined and leak-free. To me, this is the minimum ideal--it may never be definitively achieved, but one should aim for no less. Then, all manner of code abominations can be hidden and compartmentalized. Various components can be improved and cleaned at will, without rippling out destructively throughout the codebase.
This means some shortcuts are not allowed, and time to delivery will increase slightly. But those are the shortcuts that create spaghetti-code and tend by far to incur the greatest debt. So I see this simple minimum bound as a good 80/20 tradeoff for maintainability.