You mistake simplicity for performance. Simplicity is about lack of interleaving of abstractions, it's about one concept, one task, one role, single responsibility etc. I recommend Rich Hickey's talk "Simple made easy" for that matter: https://www.infoq.com/presentations/Simple-Made-Easy
Performance is faster execution and lower resource consumption. Perhaps this isn’t so much a factor anymore with low level languages, but in high level languages with several layers of abstractions and giant frameworks there are huge opportunities for writing faster code.
