Assuming that LLMs hamper gaining true experience and mastery of a language, and further assuming that LLMs will play a significant part in development (especially for juniors)… it seems to me that new programming languages and frameworks will have a significantly greater hurdle to overcome going forward, compared to what they faced in the past.


I don’t think this is linearly correlated. Despite being called a “Language Model”, it does not mean it processes language as humans do. If an LLM is good at supporting you with a programming language mainly depends on the amount of available training data.
Let’s take esoteric languages as an example - there are languages that only work via weird Unicode symbols or other cryptic commands. A human will have a hard time to understand that language, the LLM may not have any problem at all to give working comprehensive examples (as in will be useful).
Time to conquer Malbolge with ChatGPT.