This has always been true. LLMs didn't change that.
Spend any amount of time, reading the implementation of powerfull algorithms (A* search, Bubble sort), and you will realize that the power is in the idea, not the feeble attempt at coding it in PHP, Go, JS or what ever.
But what if the three senior devs could produce thousands of lines of great code that implement thousands of features perfectly. I don't think this is the case but I believe this is what the OP means.
the interest is of course because what "the business" wants is thousands of features, perfectly or imperfectly is a secondary consideration.
on edit: changed senior devs hundreds of thousands to thousands because one benefit is that much of the code the average make is not really needed.
You are comparing senior vs average devs here. What will happen if a team of 'two or three senior devs' with AI/ML tools compete with equally skilled 10 senior devs with AI/ML tools?
I don't think we need to wait for 2030. Today, using aider/cursor and Gemini-pro-2.5, I'm pretty sure a team of two or three senior developers with great domain knowledge would be competitive with a team of 10 average devs. Being a small, close-knit team has a lot of advantages. And LLMs can help close the productivity gap.