Presumably the "fresh Phds" getting 300k right out of school have extremely relevant experience and are quite capable of actually putting their learning to use

Presumably the "fresh Phds" getting 300k right out of school have extremely relevant experience and are quite capable of actually putting their learning to use (I don't have data to prove this). People who just know TF and couldn't implement it and know what it does and doesn't do well aren't the kind of people attracting 7 figures. There's a huge amount of advanced statistics, math, and "intuition" that takes years working with data to build. Abstractions like TF (etc.etc.) make applying existing solutions to existing problems more tractable, but the real gold-rush is happening around the new/relatively-unsolved problems.