Here is the thing: many software engineers don't need to learn a language "properly."
When you start a new job, there will almost always be an existing code base, and you'll have to make contributions to it. Pattern recognition will get you a long way before you need to dive deep into the language internals.
You are mixing two things. Learning a language and learning a codebase. Those are not the same thing. Besides, you are also just talking about what happens during the first N months. Most companies I've worked for allow for time to learn the language(s) being used. Some of them will fire you if you can't show sufficient progress over time.
Not so much. I know quite a few languages very well, more than the average programmer, and more often than not a senior programmer overrides your recommendation and don’t know the language as well as you or some other red tape. What has never happened is getting an increase in pay for knowing a language well.
So I share the sentiment that learning a language well is valuable. It’s not, and with the newer AI tools coming out there will soon be no reason to learn any language in depth.
I think you have that exactly backwards. LLM-based tools do best on shallow-knowledge tasks. It’s depth where they struggle. Show me the syntax for constructing a lazy sequence in your language? LLM. Reason about its performance characteristics and interactions with other language features? Human, for the foreseeable future.
When you start a new job, there will almost always be an existing code base, and you'll have to make contributions to it. Pattern recognition will get you a long way before you need to dive deep into the language internals.