That's a very valid concern.
My personal opinion:
Yes, the package system is pretty small. That's why it depends what kind of project you are gonna write and how much time you have. Ruby has a lot of gems, but many of them are buggy and deprecated... Proof: https://github.com/rubysherpas/paranoia
I think that Elixir is gonna catch up. If you write a project where you need to use a lot of external libraries probably Ruby is better. If you don't need to rely on the external dependencies too much and you want to/have to write your own code(libs), imo, Elixir is a better option. It also depends on a project, lots of external api calls, webhooks, real time chatrooms, etc. I think Elixir is gonna be a better option.
One thing more, because Elixir's code is much easier to deal with, it's easier to fork and fix deprecated lib than in Ruby(Rails).
In addition, Elixir libraries tend to be very high quality in my experience. This is not the case with gems; I'm always very hesitant to add a new dependency in my Ruby applications.
Of course, the quality disparity exists in part because there is a much wider pool of developers with varying levels of experience in Ruby, similar to Node.js. But I believe Elixir encourages and even enforces a certain level of code quality, without introducing fragile mutable state, security issues, and package incompatibilities. Thus I expect the quality of Elixir libraries will remain high even as the pool of Elixir developers grows.
Another concern with Elixir is that, like Node, it is optimised for IO, not computation. Take chatbots, for which Elixir is supposed to be ideal - what if my chatbot connects to a computation-intensive AI/NLP model. I'm going to need something else for that, surely? Elixir and Node are good for the orchestration layer but lack the all-round capabilities of, say, the JVM platform.
Elixir definitely comes up short on raw computation. However we've been very satisfied with it for implementing a database. Use data oriented design (you want that anyway) and move any CPU intensive part into a native function. It's pretty straightforward to bind a C/C++/Rust library.
Considering the massive growth in AI that makes Elixir only half a solution then unless you're good with low-level languages such as C/C++/Rust. Scala and Clojure, on the other hand, are good for both computation and IO so I don't really see the advantage of Elixir.
I think that Elixir is gonna catch up. If you write a project where you need to use a lot of external libraries probably Ruby is better. If you don't need to rely on the external dependencies too much and you want to/have to write your own code(libs), imo, Elixir is a better option. It also depends on a project, lots of external api calls, webhooks, real time chatrooms, etc. I think Elixir is gonna be a better option.
One thing more, because Elixir's code is much easier to deal with, it's easier to fork and fix deprecated lib than in Ruby(Rails).
It's just my opinion.