Just curious, are you mostly FE? I could see this there (but there is still a lot of browser esoteria, etc)

Doing backend and large distributed systems it (seems to me), much deeper. Types of consistency and their tradeoffs in practice, details like implementing and correctly using lamport clocks, good API design, endless details about reworking, on and on.

And then for both, a learned sense of what approaches to system organization will work in the long run (how to avoid needing to stage a re-write every 5 years).