I worked extensively in the parts of the Figma where Evan wrote a lot of foundational code, and have also worked directly with him on building the plugin API.
One of Evan's strong points as a CTO is that he was very pragmatic and that was reflected in his code. Things that could be simple were simple, things that needed complexity did not shy away from it.
While all codebases have early decisions that later get changed, I'd say that largely speaking, Figma's editor codebase was built upon foundations that stood the test of time. This includes choices such as the APIs used to build product code, interact with multiplayer, the balance between using OOP v.s. more functional or JS-like patterns, the balance between writing code in C++/WASM v.s. JS, etc. Many of these choices can be credited to Evan directly or his influence.
Subsequent engineers that joined were able to build upon the product without causing a spiraling mess of complexity thanks to those good decisions made early on. In my opinion, this is why Figma was able to ship complex new features without being bogged down by exploding tech debt, and a major contributing factor to the business's success as a whole.
