Not to say every person should have a silo-ed portion of the codebase that nobody else ever touches or understands. I just think the pendulum has swung too far

Not to say every person should have a silo-ed portion of the codebase that nobody else ever touches or understands. I just think the pendulum has swung too far in the other direction. Yes. It's one of those mythical management "best practices" that never actually happens because it doesn't work. Most interesting software development involves creative thinking. Unless someone finds a way to download the entire thought process of the original developers and losslessly transfer it to other developers later you can't recreate 100% of the knowledge and insights that came from the original development work. What you can do is acknowledge that your developers are individuals with unique knowledge and abilities not just in general but because of their history within your own organisation. Value the unique experience they collect while working with you and - for as long as they remain with the organisation - encourage them to actively support colleagues who are later working in the same part of the code. There is no substitute for retaining that knowledge and having the original source directly accessible but of course most people do move on eventually. So it's also a good idea to emphasise good design and coding and documentation practices so that even when the original developers move on and you'll never have access to the ideal source of knowledge again you still have enough to figure things out when you need to. The fallacy is the idea that working that way will ever be comparable in productivity to having the original source still around and willing to help.