But software development also often seems to have a strong thread that if you don't also do this for fun, you're not really A material--in a way that really doesn't apply to other engineering disciplines.

Software scales differently, that's why software companies that benefit from that scaling pay so much for top talent.

I can't think of an area where being hyperfocused on your discipline isn't viewed as a a given to get to the top. It's just that most engineering positions that I know of don't care if you're the best to do X, and are more "can you do X". Equivalent to enterprise 9-5.