Knowing how to code well is of course very important. What “well” means” though is contextual. Are you coding an operating system, a machine learning algorithm, a http api or a full stack website? Each context requires different skills and a different way of thinking.

To say languages don’t matter however is misleading. If your goal is to write a high performance database engine and you attempt this in python, Ruby or PHP then the results will be dismal. Likewise if you try to write a highly concurrent http api in assembly you might die before you finish it.

Language choice impacts performance, coding efficiency, tooling, ecosystem and long term maintainability. All these things matter.