This is very true but there's still is a very big difference between knowing languages like JS, Python, Ruby or Go but then jumping into a place that uses Elixir or a niche language that's different than a lot of other popular languages.
For example I took a position to do mostly infrastructure work. Most of their services are written in PHP which I haven't used since the early 2000s. I wouldn't classify myself as a PHP developer. Sometimes I find myself diving into the code to self-solve issues I have that are infrastructure related. My thought process is if I can solve a problem and it's within my scope of things to do I'd much rather just do it than add extra work to another developer on the team. In the worst case scenario someone with actual PHP experience who does the code review will offer suggestions to make the code better.
I don't really know PHP but I can look around and navigate the code without issues. There's nothing that looks too foreign and the code is easy to grep to find stuff. It's also not too bad to trace code in a large app and understand the logic. There's also a massive amount of Google results for almost any problem you can think of. It really means for a lot of cases you can combine previous experience and be productive in a similar language without really knowing it. Enough to contribute real code that gets shipped to production.
I ended up doing this yesterday where I added an IP whitelist address exempt config option to one of our apps. I wanted to at least toy with the idea of doing IP range detection within a CIDR block.
In Python this is really easy, the standard library has functions to do this with 1 line of code. Ruby's implementation is even easier and built into the language. For PHP I had to Google around but found a pretty small custom function to use in less than 2 minutes. For Elixir? Well you have to use a 4 year old+ third party dependency or dive down into Erlang and understand pattern matching and write a bunch of code to manually do the comparisons. Maybe there's a good Elixir solution but it wasn't on the first 3 pages of Google when searching for similar terms as I did for Python, Ruby and PHP. Weirdly enough if you search for "elixir check if ip address is in cidr block range" most of the top results are StackOverflow posts for other languages. There's no contest in comparing the amount of effort it took to get a solution.
I know this is 1 just example but I also know when I tried learning Elixir (and did end up writing about 10k lines of code of it) I kept running into situations that took half a day or longer to figure out while actively trying hard to learn and use the language. These problem could be fully solved in a production ready way in 5-10 minutes with Python or Ruby (and I guess PHP too) either by knowing how to solve it in an imperative way or finding nearly a perfect solution when Googling that's digestible enough to where you can fully understand it and apply it back to your problem.