I have tried many (all the popular) huggingface summarization models, they don't compare to GPT. Basically, they highlight the parts they think are important. But they can't "understand" and generalize.

Frankly, I haven't read the papers about summarization. But I will have to when I'll work on reducing costs.

I see, thank you for the insight. The OpenAI paper about summarization is an easy read and very similar to your approach, if you are looking for somewhere to start: https://openai.com/blog/summarizing-books/.

That’s commonly referred to as abstractive vs extractive summarisation