I didn't say they can't function as an individual contributor. I said they can't function efficiently as one. Meaning: the opportunity cost would be too high, since the alternative is that they help their more junior team members grow and also help the company make the right decisions when it comes to things like system architecture, tech stacks, features, etc. Those types of contributions can be several times more valuable to the company.

Maybe what John is getting at is while a Principal can do that for a while, at some point their tech chops will get out of date and rusty, both in terms of industry knowledge and the company’s internal stack and best practices. At that point they may lose the respect of more junior engineers, which is a poor sign for company culture.

A senior IC that codes can stay relevant longer. The act of coding forces you to keep up.