PHP, Perl and Swift all have first-class functions, lambdas and closures although I'd agree that that's not "most." This is probably getting too much into semantics, but aren't functions in JS just objects themselves? ;)
>People stress about "writing unit tests" because technically correct types doesn't mean your program actually works. In my time writing JS vs TS, I've seldom found that type errors were the problem aside from making the type checker happy. Most errors are in what the code actually does or does not do. The instant feedback from the entire system is far superior to unit tests because it can catch things that your unit tests might not be testing for.
I don't think having a "live" system like CL precludes the need for unit tests. Sure, it's beneficial to be able to play around with code right away, but unless you're planning on manually running through the same tests again and again, how do you know you've not introduced a regression at some point?