> It’s a pretty safe assumption that the people who worked on the codebase before were as smart as you.

Amen! Code is never written in a vacuum. Code is never shaped only by engineering but by business and organizational compromises as well. I hate those guys who declare we absolutely must do sweeping changes to the codebase/architecture so that we are in line with the latest best practices after spending an hour with the codebase. As if the guys who spent the last 3+ years staring and building on said codebase didn't know any better (unless of course you were hired specifically because you ought to know better!).