Perhaps you're measuring value too narrowly. A principal engineer can act as a force multiplier for the entire team, even if they themselves are no longer efficient individual contributors.
A senior IC that codes can stay relevant longer. The act of coding forces you to keep up.
His answer is: on high leverage activities. Instead of fixing a small bug that affects a few customers, fix a big one that impacts revenue; train others to be better engineers, multiplying their future output; improve the process your team uses to build product. Essentially, look for activities that multiply output, rather than add to it.
Gandalf in the battle of Minas Tirith is a huge force multiplier. He embiggens the courage of everyone near him and makes them fight harder and better.