https://xkcd.com/1053/ is relevant. The world would do well by adopting a more positive perspective towards people who don’t know what we expect them to. Because I’m sure, they probably know something I don’t… that they expect me to know. And that’s how we all progress.
I think focusing on mastering the fundamentals in depth would pay off for any software engineer, with benefits that compound every decade of your career after putting in that upfront time cost and a fairly minimal maintenance cost.
Do some ideas have higher leverage than other ideas: certainly. Is it easy to tell a priori which ideas those are: not entirely.
Consider log-structured merge trees (LSMs) were invented in 1996; Amazon S3 was released in 2006. Some might consider these fundamental ideas that have existed for 28 and 18 years, respectively. Have you mastered these ideas enough to understand how the cost structure of S3 enables you to implement a really economical distributed LSM at extremely low cost because S3 doesn’t charge you for bandwidth usage?
The point of the fundamentals as commonly construed is to allow you to quickly pick up novel concepts as needed as they're almost always a slight extension of the fundamentals.