I agree. I will paraphrase this as - a well designed language should be usable, at minimum, from a pure text editor, and should not put unreasonable burden on an IDE.
The cynic in me wants to say that such a language doesn’t lend itself to static analysis. As soon as you can do great things with static analysis you can build those features into an IDE, therefore causing the “pure text editor” to feel crippled giving rise to the idea that this language is “unusable from a pure text editor”.