I've worked on teams of various sizes and skills writing OO applications and trying to use inheritance and OO to get code reuse is always a nightmare. I currently work on large project with hundreds of Scala engineers of various abilities, and structuring our code in functional ways has bought us a ton of reuse and prevented a lot of technical debt.

We primarily write libraries, and our 'applications' are more or less throw away code because of how small they end up being (because they can leverage many of our libraries). Testing is easier in functional land (for various reasons), which means regressions are much harder to introduce, which means refactoring can happen faster, which means less technical debt.