> Then let me explain. While some programmers (~10% by my educated guess) like languages with lots of features, but most don't; really don't. It seems that being able to serve as a first language is a prerequisite for being super-popular (and Java, Python and JS serve in that role), and having more features is a big hindrance to that. We are more concerned with Java having too many features than too few (and teachers complain about that).

Programmers want to deliver working code. If that code needs to be asynchronous and handle data, they'll use whatever is easy, acceptable and available to use with their language. That "feature" may be provided by the language, by a compiler, by IDE code generation, by a pre-processor, by a post-processor, by runtime code generation or by a library that is using some idioms.

Most programmers (my educated guess is 80%) don't care very much how they get that done, as long as they can get quickly learn it and get stuff done keep their managers and co-workers are happy. Programmers need to go through a learning curve to learn new features, whether they are library features or language features. A language can "cheat" a little by keeping itself lean and mean and deliver data class creation to IDEs and annotation processors, while letting libraries implement concurrency and even coroutines (see Quasar for Java and Greenlet for Python).

This doesn't remove any complexity from the programmer dealing with these languages. Some times it could make the programmers' life even more miserable since there are multiple competing methods to choose from.

Having led programmer teams working in both C# and Java, I can clearly say that C# programmers are less confused by data classes and concurrency issues. I wouldn't say C# is perfect (C# properties are messy and their async/await implementation is pioneering, but somewhat confusing). I don't like all features that get added to C# either, and I sometimes think Microsoft could exhibit more care here. But I feel less "burdened" when we have to use C# (or Kotlin, Go or to certain degree Rust) for concurrency and asynchronous I/O rather than using Java and JavaScript, which have way too many historical ways of doing the same thing.

I think you're thinking too much from the perspective of a _language developer_. Language developers like less complexity in their languages, and that's totally understandable. But developers don't care so much about that, and despite what you say, I don't think there's good evidence that this is what makes a language extremely successful. The process of a language becoming successful is a lot more complicated than that and I doubt if it can be easily described. After all, the historical data we've got is too sparse. But if we look at languages that did become successful before and after Java, most of them were quite complex compared to their competitors:

PL/I was considered extremely complex and bloated in its time, but it became popular nevertheless, since it had a strong corporate backing from IBM. The very same company, incidentally, was one of the largest corporate backers of Java since the early 1990s.

While C was arguably almost as lean as Pascal (if not as easy to learn), it barely got any foothold in the world where Java has won so decisively later: Enterprise line-of-business software. These programs tended to be written mostly in COBOL and PL/I on mainframes, and on the PC developers used whatever was available, including assembly. Smalltalk (not a "simple" language for its time, considering the _entire_ package you'd get) also had a short heyday. But when Java came out, the world settled on C++. Sure, C++ back then was less than the shining paragon of feature creep that it is today, but it was still a rather complex language. The various dialsects of object-oriented Pascal were simpler. Modula 3 was simpler. Smalltalk was probably simpler too. But C++ won.

In the defense industry during the 1980s, Ada was queen. The reasons for this are really simple: this was often what the DoD mandated. Just like many corporate IT departments mandated Java years later. Anecdotally, all Ada programmers I met loved the language back then. They didn't lament the massive amount of features (for the time).

Embedded languages are also an interesting case. Small languages like Lua are quick objectively easier to embed and you'd think they'll win decisively. Lua is quite popular as an embedded language, but it seems to be on par with Python and losing to JavaScript.

Why did JavaScript become so popular? It's certainly not a simple language. There are many complex features that are not used very often like proxies, generators and all the various Object functions. There are often several layers of historical cruft or different solution strategies, such as prototypes vs. Object.create() vs. classes. Or "Error(...)" vs. "new Error(...)" or var vs. let. Or this-binding arrow functions vs. traditional anonymous functions and Function.prototype.bind(). Equality laws type coercion are famous bonkers[1]. Even from its very inception, JavaScript was more complex than necessary, and made some decisions that kept annoying generations of developers (e.g. vars and prototypes). And it still won, since Brendan Eich got included in Netscape and Microsoft rushed to copy it with (the frustratingly randomly incompatible) JScript. JavaScript never made developers happy and still has a certain type of fatigue named after it.

> the objective fact is that no language with a strategy of adding features quickly has performed better in the market than Java

This is deductive reasoning from a single datum, where there are many other social and technological factor that could determine language success. The fact is that before Java, the most successful languages - especially in the same industry Java rules most strongly today (business programs) - have been rather complex: COBOL, PL/I, C++. And to the best of my knowledge, they all had strategy of indiscriminately adding features in the language level.

I fail to see any strong evidence to your claim, while there is some anecdotal evidence to the contrary.

>> But I disagree with the stance that stackful coroutines are superior.
> Okay. There aren't many things all developers agree on.

That's great, but then it's just opinion. I personally prefer stackless coroutines, but I won't go ahead say they're strictly superior to stackless coroutines. There's a reason many languages still chose to go with stackless coroutines even though stackful coroutines are far from new. Swift has added async await quite recently an I'm pretty sure Apple was fully aware of the work done on Project Loom, Go, Lua, Erlang and many others. Microsoft could have very well chosen stackful coroutines for C# and implemented them to be transparent like virtual threads. gevent was doing the same thing (in a more primitive way) in Python after all. It's not like stackful coroutines are a new kind of tecnology we had to sit and wait for years to research properly.

[1] https://www.destroyallsoftware.com/talks/wat