Been using llm for following usecase
Big llm like Claude and gpt for coding help
Copilot for coding
Local llm like mistral2 for
1. Parsing LinkedIn posts to find jobs and put them in Google sheets
2. Mental sparring by giving local llm a problem and asking it to ask important questions instead of answer. This helps me identify if I have thought it through or have i missed some things
Imo it's about learning base concepts which remain the same and get utilised in bigger systems more forcefully. It's similar to learning algo and ds we might not get to use them in our current work but people in places use them and need them.
Coming back to system design, when I say concepts i mean design patterns. Like two different rate and capacity systems are coupled using buffering systems etc.
Good resource for this is Microsoft system design blog series. Go through them , they have standard problems and scalable solutions that can be adopted.
Another part of system design is distributed systems, how do you attack distributed system design again learn the design patterns that are frequently utilised in distributed systems.
How you can learn that is via excellent blog series and book by unmesh Joshi of thought works.
If reading is not your medium then there are ample video series on YouTube.
I've used sailsjs multiple times and once I'm up to speed with its concepts, the dev time is really really fast . It doesn't fit some of your parameters