language is hard to read

for item in array do
  puts item[:name]
end

Whew, iterating and working with data in Ruby is so hard. How does anyone read this stuff.

low performance

Ruby is a syntax-sugar-loaded C-wrapper, just like Python and countless other languages that don't compile straight to machine code. If anything other than C and Rust are slow to you, then sure, maybe Ruby isn't a good fit for your project (but Crystal might be).

create your app fast

Damn right, I'm two or three times as productive as I ever was in C#/Razor, Java/Spring or kludging through the countless JS boilerplate-heavy web frameworks.

but then maintaining it is expensive

As with any app that grows into something successful and widely used, technical complexity becomes exponential. I've found once web applications grow to a certain number of models and controllers, the relationships between them start to grow exponentially as well. This means one small change can ripple throughout your application and have unintended consequences where you least expect.

This is not even remotely a unique problem to Ruby. It's happened across every project I've seen that grows beyond 30 models and a couple of dozen controllers, regardless of language. This is why unit testing is so important.

But, specifically you mentioned you can't "onboard new developers easily". I don't see how. I've taken two CS grads straight out of college and had them adding features with tests within a couple of days on Ruby projects. Ruby was designed to be most friendly to humans, not the compiler. If Rails is what is tripping you up, imagine trying to learn a new web framework on top of an even more complicated language than Ruby. I just don't see this argument at all, from my experiences.

Ruby’s creator finding the situation of his language being popular because he’d created it as an experiment

Pretty sure most any language that was created by an individual and not by BigCorp™ is a feat in and of itself. This speaks more widely to a language's capabilities and value if it can reach popularity without corporate backing. This argument seems to imply that because of it's origin, it will always be some kind of experimental toy that was never intended for wide-use.

Meanwhile, Linus Torvalds:

I'm doing a (free) operating system (just a hobby, won't be big and professional like gnu) for 386(486) AT clones.

Things have to start somewhere, I guess?

I kindly ask you to be more constructive in your criticism of Ruby. It's a great, powerful language with a low barrier to entry. There's no reason to spread FUD about it.