Well, I've gone through SICP (book and exercises), so I might say that I have some familiarity with Lisp, as well as Python - but it's one thing to do toy or pe

Well, I've gone through SICP (book and exercises), so I might say that I have some familiarity with Lisp, as well as Python - but it's one thing to do toy or personal projects and another altogether to work on a full-scale project with several collaborators and a complicated history. There's a whole class of issues you experience in such a project that really shed a new light on a language as a tool of communication between developers. By the way, the speed I mentioned is speed of development. Both Javascript and Python are used nowadays in speed-critical applications, with NodeJS on the servers and Python in various roles in big data and machine learning because the critical path is actually done on C level (I/O for NodeJS and GPU/math stuff for Python) while these languages are in charge of the stuff that is not that critical in terms of speed but much more complicated in terms of logic. This brings me to think that if you use a language on an appropriate domain and separate concerns between domains in a good way, it wouldn't matter if the language itself isn't that fast.