I love Elixir, Erlang, and BEAM, but tbh, not crashing is a fairly well solved problem in the web world regardless of language and runtime, in large part due to the request/response nature of things.
I am not the best Python programmer! I have crashed prod before, I will admit it. And this requires an alert, scurrying to the nearest terminal, an SSH console, some log spelunking, hopefully just a restart. But I have never had this experience deploying Elixir or Phoenix, and I am by no means the best Elixir programmer. Firefighting is to me the worst part of programming, and through a combination of interactive Elixir shells, process isolation, automatic process restarts, and a philosophy of "let it fail, it's no big deal," it has brought some joy back into my work. That alone is priceless!
I understand Elixir can seem overhyped, and I share that skepticism, but I keep coming back to it over the last half decade or so. This is the best endorsement I can give, I think.
So in an ideal world yes, you can isolate them, but I've never really achieved this panacea in practice, and its never been anywhere near free to try to suss out a design that optimally achieves all those differing design aspects at once.