Okay, but we can always replace "slow" by "slower than" and in a desktop environment (which the article is about), we could still compile C++ code to run native

Okay, but we can always replace "slow" by "slower than" and in a desktop environment (which the article is about), we could still compile C++ code to run natively and outperform JavaScript any day. The whole brouhaha about JavaScript being fast stemmed from it suddenly not being 10 times slower than native code in benchmarks. But it's still slower. By using JavaScript you are, out of the box, sacrificing about 20% of your performance for the comfort of using it. In some cases, maybe only 10%. In others 50%. I can totally understand how that's a trade-off one is willing to make in many cases. But for desktop apps, I kinda want them to run at full speed. Like, a 0.2 second delay can get annoying if it comes at the wrong time or stacks with something else. And somehow, you can feel that in many hyper-modern apps that are so many layers removed from the hardware, the devs probably don't even know where it touches it.