It's clear to me when I am reading things as sight words and when I'm sounding them out, especially when reading aloud - if we're looking up a medication, for example, and reading it to each other, we'll breeze through the stuff about take it before breakfast with a full glass of water and then slow to a crawl while sounding out the generic chemical name of the med.

I don't usually notice at all, but you're right that the medication example is a really good way of looking at it. It's all about the phonics there!

I find that I'm trying to make sight words out of what I see rather than sounding them out, even though sounding out is much more straightforward in Hangul than in English

That's so interesting!

I think people very much do read Hop on Pop (in fact, I read it to my niblings just last week!) and it's that kind of thing that I feel like should be a foundation for learning to read.