First of all, the other programming environment like it is Pony. Although that's barely a C-list language right now, very young, one to keep an eye on though.
I'd also cite the real technology I'd use today, which is a heterogenous set of services in whatever languages I'd like, hooked up by a high-quality message bus. This is the real technology that drives the at-scale Internet. You basically get Erlang's reliability out of that setup when used properly, and you don't need Erlang to do it. In fact you can get a touch more than Erlang's reliability because I find in practice 1-or-n delivery to be much more practical than Erlang's 0-or-1 delivery. It's basically the same enviromnent Erlang gives you integrated, except decoupled, and since all the pieces are decoupled, while Erlang has sat on the same effective point in this space that it picked out 25 years ago, all the decoupled components have been iterating and evolving over that time frame and are now better than what Erlang offers in its integrated package.
Second of all, if in 2021, around 25 years after Erlang and easily 15 years after Erlang has been generally known as a B-list language among language designers, almost nobody else has seen fit to copy it... maybe it isn't that great of an idea. Rust does something completely different, and in my opinion, strictly more useful, albeit at the cost to programmer complexity. I moved to Go from Erlang roughly 8 years ago, and I'm happier, because it turns out "general community good practices + channels" is fine, and also means I can go faster, and get a nicer language in the meantime. All the other modern languages are coming with some sort of concurrency story; it's table stakes for any language born in the last 10 years, if not the last 15.
For the mid 1990s, it was sheer genius. For 2021, it's a very brute-force, inelegant solution to the problem that nobody's very interested in copying. While in the 1990s concurrency was a nightmare and Erlang legitimately had a claim to a better solution, in 2021 there's a good 3 or 4 things I'd use before dropping back to Erlang as a solution. Concurrency is much less of a problem than it used to be, through a combination of various things, and the proposition of burning so much of a languages design budget on that problem is a lot less appealing than it was 30 years ago. Erlang really needs to adopt Go-like channels for some of what it's doing (not in replacement for the processes, but for some of the things they're not very good at), the ~10x slowdown for general logic is a real kick in the teeth in 2021, the lack of backpressure in the Erlang message model becomes a big problem at scale, and lots of other little problems I'd have if I had to go back to it. (Yes, I've been reading the release notes. If I weren't I'd have a couple more things to add.)
Erlang/Elixir/BEAM isn't leading the pack anymore. They're a cut behind in most ways now, but the community still thinks they are leading, ensuring that none of the lessons learned by other communities can filter back into the Erlang/Elixir/BEAM community.
Even if I disagreed with you on another comment I'll have to say that I find myself much more in agreement with you here.
Erlang / the BEAM did indeed make a lot of good innovations and I can only be angry at myself for being an idiot pressured by employers and never looking beyond it all for something better (until 5+ years ago anyway). But I agree that some of it is starting to show cracks.
In terms of language design, Erlang (and Elixir) aren't anything special. I can't fall in love with syntax anymore because I've literally never seen a language I completely like (LISP included, although it + OCaml are fairly close to ideal languages if you don't stray too much off of the beaten path and venture into their more arcane constructs, of which OCaml sadly has plenty).
To clarify, I believe Elixir is one of the most solid contenders for writing highly available and reasonably performant Web / GraphQL server apps but the lack of compiler apparatus tooling, tooling to modify AST and a few others are definitely starting to hurt it. Having standardized introspection in the language helps it reach higher levels, e.g. have tools that can manipulate an existing project a la like TreeSitter and/or SemGrep can modify/query language-specific constructs. Elixir doesn't have that and I am starting to get annoyed with it because of that.
RE: Using an external messaging bus makes sense but let me point out something important that seem to be often not said in discussions about Erlang / Elixir:
The BEAM gives you a lot of good training wheels and the truth is that at least 90% (if not 98%) of the commercial projects out there don't require much more than that. As shared in the other comment, I was able to get away with not using Redis for a long time and had zero trouble. I only yielded after we needed to share various message queues and events/streams with other apps (not written in a BEAM language).
So I'd say the BEAM ecosystem gives you a lot out of the box, plus the Elixir community is small but fairly dedicated and they have libraries of excellent quality. But, as you alluded to, when you need to throw those training wheels off, other much more dedicated and focused technologies like Redis do exist and we should reach for them after the circumstances change enough.
I'd also cite the real technology I'd use today, which is a heterogenous set of services in whatever languages I'd like, hooked up by a high-quality message bus. This is the real technology that drives the at-scale Internet. You basically get Erlang's reliability out of that setup when used properly, and you don't need Erlang to do it. In fact you can get a touch more than Erlang's reliability because I find in practice 1-or-n delivery to be much more practical than Erlang's 0-or-1 delivery. It's basically the same enviromnent Erlang gives you integrated, except decoupled, and since all the pieces are decoupled, while Erlang has sat on the same effective point in this space that it picked out 25 years ago, all the decoupled components have been iterating and evolving over that time frame and are now better than what Erlang offers in its integrated package.
Second of all, if in 2021, around 25 years after Erlang and easily 15 years after Erlang has been generally known as a B-list language among language designers, almost nobody else has seen fit to copy it... maybe it isn't that great of an idea. Rust does something completely different, and in my opinion, strictly more useful, albeit at the cost to programmer complexity. I moved to Go from Erlang roughly 8 years ago, and I'm happier, because it turns out "general community good practices + channels" is fine, and also means I can go faster, and get a nicer language in the meantime. All the other modern languages are coming with some sort of concurrency story; it's table stakes for any language born in the last 10 years, if not the last 15.
For the mid 1990s, it was sheer genius. For 2021, it's a very brute-force, inelegant solution to the problem that nobody's very interested in copying. While in the 1990s concurrency was a nightmare and Erlang legitimately had a claim to a better solution, in 2021 there's a good 3 or 4 things I'd use before dropping back to Erlang as a solution. Concurrency is much less of a problem than it used to be, through a combination of various things, and the proposition of burning so much of a languages design budget on that problem is a lot less appealing than it was 30 years ago. Erlang really needs to adopt Go-like channels for some of what it's doing (not in replacement for the processes, but for some of the things they're not very good at), the ~10x slowdown for general logic is a real kick in the teeth in 2021, the lack of backpressure in the Erlang message model becomes a big problem at scale, and lots of other little problems I'd have if I had to go back to it. (Yes, I've been reading the release notes. If I weren't I'd have a couple more things to add.)
Erlang/Elixir/BEAM isn't leading the pack anymore. They're a cut behind in most ways now, but the community still thinks they are leading, ensuring that none of the lessons learned by other communities can filter back into the Erlang/Elixir/BEAM community.