I've been searching for a decent walkthrough for this game and I keep finding the same one replicated on dozens of sites (created by somebody called "ADK19"). Frankly, no offense to "ADK" intended, but this particular walkthrough sucks big time. It is very poorly organized and leaves out a ton of key details, especially on the sub-quests. If anyone can recommend a better alternative, please do.

Yep, gaoneng's is exactly the kind of walkthrough I was looking for. At least now I know how much of the subquests I've missed (most of which I can't finish anymore). I wonder why ADK's show's up everywhere, but gaoneng's obviously superior one does not?

It's up to each author to decide where his/her walkthgough can be hosted.
gaoneng adresses this right at the beggining of his walkthrough, he doesn't want his walkthroughs hosted anywhere else.

I'd still think the internet would be full of links like yours that point to the better walkthrough, even if it can't be hosted on other sites.

I really don't know about that :)
But it's not uncommon to find some walkthroughs and indepth guides at gamefaqs that aren't available anywhere else, so it's usually a good idea to take a look there.