1) It is extremely rare for a field to ever 'be solved'. There is still active research into how to multiply 2 numbers together. NLP is not anywhere close to solved.

2) LLMs have different trade-offs to fundamental techniques. Linear regression still gets lots of use despite there usually being a theoretically better method for any specific application. There will be parallels to that in NLP.

3) Isn't the article talking about training things like LLM? It is right there - "Chapter 4: Training a neural network model".