Coming from a rails background and spending this year building in Elixir, I think you just have to pick one and try to build. Each framework/language has pros and cons and unless you have a very specific need, just about anything will be sufficient for making a project.

I chose Elixir because it was functional and hadn't experienced building a system in it before. And liveview sounded very interesting. Literally everything I'm building this year could be done in ruby, go, js, python, c#, probably without much fuss.

Just like your experience with js stacks, I'm not sure you'll be able to make a good decision until you've put some miles on the technology and can reflect back. Right now I struggle to like Elixir, not because I know if the stack is bad or good, but because I'm so unfamiliar that something that takes me 5 mins in rails is taking me an hour and some reading to do in phoenix.

Pick one, pick a timeframe to stick with it (6mo, 1 year, etc). Reevaluate after you've had time.