It is relevant because they chose to abandon best practices because of a lack of tooling. A badly chosen language constraining your development methods is like

It is relevant because they chose to abandon best practices because of a lack of tooling. A badly chosen language constraining your development methods is like a tail wagging the dog. There are languages and, more importantly, implementations out there that allow this kind of design. Just think of SML/NJ as an example for the principle. If performance is important and C# doesn't allow unit testing performant code then switch to C++ or Rust. It is staggering how many people seem to see the choice of language as an absolutely unchangeable decision. Rewriting even millions of lines of js or python code is definitely doable, even incrementally, and if your organization does not deem it worth the effort then maybe performance is not your most important concern.