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I'd agree with most of this. I feel like the decision to use the JVM is what made Clojure useful at work for me vs. other languages like Elm, Elixir, Haskell, and so on that I can only just play with at home. Elm is cool but I can't justify it professionally.

People really should not discount the importance of having a big ecosystem, at least transitively in some way (ex: Clojure -> Java/Scala/Groovy). Once upon a time I took a break from C and C++ dev to do Smalltalk. It was glorious and productive, but at the same time I had to literally write everything myself. The community, even at the height was relatively small vs. some languages today. The worst was writing low-level stuff that while I could do, gave me the voice inside my saying, "WTF why am I wasting time on this." No one should ever do that if they can help it; it just eats your time.

The only real situation that comes to mind where I personally felt justified reinventing the wheel entirely was game development (ex: custom allocators, custom pipelining, entity systems). That still was time lost I could have been using to make a game and get other things done, but there were very good reasons like performance. Console development in particular was exactly this - it's not like I could go out and ask someone for their NES libraries or even in later years, PS3. Games don't generally reuse much code and certainly not when a generation of consoles is brand new with a new architecture. I could have written code like an idiot, but I chose instead to write stuff against the platform. We did well because of it vs. competitors. You can say Engines handle some of that for my specific cases, but that's discounting that huge chunks of a game are not in fact the engine or that some games preclude the use of an engine for various reasons or engines sometimes end up having the opposite effect (ex: Star Citizen).