These languages put you at the level of writing a language for each problem domain immediately and with a comprehensive and useful toolkit. These languages also do this while directly competing with all but the most carefully tuned of C++/C environments. Steel Bank Common Lisp and the Glasgow Haskell Compiler are good references here.
These languages are often considered strange because of this, and feel somewhat alien. But once you realize you're building a language to model your problems, suddenly tons of stuff makes more sense. Previously alien concepts like Macros and Monads are outside the typical language's experience precisely because the language authors created these contexts and put you inside them.
This article is sort of fundamentally wrong that it's difficult to write small, purpose built languages. It's not, and even outside the functional and homoiconic meta-syntactic world we have seen code generators deployed regularly. Successful products and libraries are build using these techniques all the time, and with a modern toolchain it delivers excellent results. It's just that other more restricted and guided approaches are often introduced earlier in people's learning curve and sets the expectations for them subsequently.