Hand-coding only -- Probably bad, you won't be productive enough. Though _maybe_ certain types of performance engineers can get away with it since you do more tweaking instead of writing, but you'll probably want to write tools with AI.
Coded forever and now I'm adding vibe coding -- Great!
Just Claude Code vs. Claude Code but went back to learn basics -- It seems like most good engineers I've known have spent at least some time at a lower level of abstraction geeking out on assembler or whatever. I'm an SRE and did Linux From Scratch. I think part of being a good engineer is being curious enough to explore things, which will cover a bunch of things that don't strictly speaking "matter".
The question is, can you really instinctually learn the fundamentals of computer science without ever peering underneath the veil? Sort of like - I don't ssh into the linux boxes all that often, but my history of doing so was an invaluable part of being a good SRE.