The bigger cost is that it takes a lot more devs to do the same thing in Python or especially in Java. Productivity per developer is hands-down Elixir's strongest selling point, not reducing server costs.
Python and Java have a multitude of web framework authors and yet none have made anything with the capabilities and ergonomics of Phoenix. I don't think they will either. It would take features those languages lack.
> more devs to do the same thing in Python or especially in Java
i guess it totally depends on "the thing" in question, but do you have any references for that assertion? that common web framework-ish, orm-ish stuff takes a lot more devs in python and especially in java?
It takes very little effort to ask a question like this and an essentially unbounded amount of effort to answer it to the satisfaction of the asker, so please be understanding if this isn't as much depth as you're looking for. I'll answer in three ways:
The first reference for this assertion is anecdotal. I've been a professional dev for 13 years and grew up with family members and friends in the same line of work. I've seen and heard of many, many projects built in different languages and anecdote after anecdote has been in the direction of people getting more done more quickly in higher-level languages. Writing similar things in Elixir/Clojure/etc goes faster than it does in Ruby/Python/JavaScript, which goes faster than using Java/.Net, which goes faster than using C/Fortran/Pascal. You haven't been around for those anecdotes I've heard, but a public one you may be familiar with is Discord. They scaled to over 5 million concurrent users on just 7 server engineers IIRC. Two years later, at a much larger scale, they still only had 4 engineers focused on infrastructure and 40 total: https://news.ycombinator.com/item?id=19238221. How many cases can you think of where a team of 7 Java or Python devs built something equivalent?
Secondly, there's research. Google "Function Point Metrics". Most research on programming productivity is paywalled but I shared one paper that isn't on one of my first Elixir-focused YT videos 5 years ago: https://www.youtube.com/watch?v=1e2_NXLxi-E&t=412s. Obviously this isn't perfect since it doesn't include what is appropriate for what domains or how well they scale with project size. Still it's a useful data point, as are pure measures of expressiveness: https://redmonk.com/dberkholz/2013/03/25/programming-languag...
Finally, thinking from first principles, why would anyone be adopting newer languages if they didn't offer some advantages over older ones? Why would certain features, such as pattern-matching and macros regularly be adopted by languages of the past 15 years, despite being very rare in languages created in the 90s? Furthermore, why would startups—for which productivity is a matter of survival—be early adopters? The simplest explanation, in my opinion, is that there really are some productivity advantages and sometimes those advantages are enough to overwhelm the difficulty in learning something new and working in a smaller ecosystem.
Python and Java have a multitude of web framework authors and yet none have made anything with the capabilities and ergonomics of Phoenix. I don't think they will either. It would take features those languages lack.