I'm truly sympathetic. The simplicity of the microcomputer era has a certain romance to it, especially if you never lived through the reality of it. There's a sense of freedom to the model of computing where only your program is running and the entirety of the machine is your own little playground. So I get why people make stuff like PICO-8 and uxn.
I agree with the criticism of Jon Blow's rhetoric, even though the tone is harsher than strictly necessary. Blow's criticisms and proposed solutions seem overly opinionated to me, and he's throwing out the baby with the bath water. He describes things like compile time and runtime hygienic macros like they're a new invention that hasn't existed in Lisp since before he was born.
However, I think targeting uxn is unfair. Uxn would be viewed better as an experiment in minimalism and portability. I think of it more like an art project.
It's unfair because the author is comparing mainstream languages that benefit from countless users' input and innovations over the course of 60 years to a niche system with a small handful of developers that has existed for maybe 2 years or so. That's a strawman if I ever heard one.