Completely anecdotally, but the most productive I've ever been in a company has been was a company in 2016-2019 who was on a monolith .ENT Framework with no kube/container setup at all.
Sure, it felt like absolute chaos some days, but I"ve never felt more productive and in a flow as then, mainly because we weren't chasing the latest and greatest thing but focusing on what's working for us and perfecting it.
The sad thing is that in many cases working on such a system is a career killer. Nobody wants to hire you. Some years ago a colleague and I realized that our company wouldn’t hire us judging from the job descriptions because we worked on systems that had been working for years but weren’t shiny. Since then I always something new to every project. Not because it makes sense but because it’s good for the resume. Other groups are even worse. Three devs writing 13 micro services on Kubernetes for maybe a thousand users ever.
It's not a career killer, it's a specialization. Focusing on nodeJS JS/TS frontend+backend stacks will equally disqualify you from .NET/Spring shops (against an equally qualified applicant, at least). The same goes for making the switch to gamedev or systems dev from many years webdev (you can do it, but you'll probably be dropping back down to a Jr or Mid-level IC position), going from COBOL/Erlang/Rust to another stack, doing Salesforce (or other CRM/specialty software) development, etc.
It's going to happen to anyone after 10-15years in the industry.
You are right that this is specialization but it still is a career killer in the case that you specialize on a completely obscure technology which will not help in your future career.
I think this fear is not entirely wrong, but is significantly overblown. There's a significant gap between what job descriptions ask for and what companies will actually hire. A resume full of dead technology isn't going to help you ladder your way up to bigger and higher-paying roles, but it's also not going to make you unemployable.
A resume full of less-shiny but still relevant technologies, otoh, has a lot of potential. You have fewer places to look for jobs, but you're a lot more exciting to the places which do want your skills.
When I look for a new position, I try and make sure it’ll allow me to learn a new fundamental skill rather than the latest new framework (though often there’s overlap:)
Over 30 years that’s allowed me to be employable across a lot of different tech stacks.
After 20+ years of maintaining what amount to monoliths and services, I wonder whether I'd be hirable if I had to find a job at some big tech company. But I think the problem-solving ability you need to manage server clusters you built yourself translates into the ability to handle whatever their cloud junk looks like. Hopefully I'm never in that position, though, because I would absolutely hate a job like that.
I can only talk from my limited experience. The company I mentioned was my first workplace outside of university, and since then more than doubled my salary. So I don't think of it as a career killer, but instead a stable environment to get yourself skilled up in what it's _actually_ like in a dev role.
