LoS has the key advantage that the story is usually at least hanging around near the action, LoI has whole stretches where absolutely nothing is happening in terms of story.
"Hey there, Leon. Walter has stolen your shit and you need this whip and alchemy and alchemy and alchemy and also this box of exposition. If you want to free your friends, solve his House of Sacred Remains!" 
<walking and pushing of organ stops ensues as Leon ponders what on Earth a vampire has a House of Sacred Remains for anyway>
"So hi there I'm that one boss from R-Type."
"Hey there, do you have something to do with the actual story?"
"Naw, I'm just chilling in this room that has nothing to do with the theme of the rest of the level and doesn't look like it either."
"Oh."
Zobek's narration is kind of handy for finding out what This Place has to do with That Place You Were Just At and what you're actually doing there, even if it does sound like he's lusting after Gabriel half the time ("he doesn't see me following him...Yes, Gabriel, DO your ab crunches!"). Aside from all the eco-nonsense (yes, man is encroaching the hell out of nature, it's only 800 years until the Industrial Revolution after all) and the rather pointless addition of the Ancient And Powerful Race That Has No Real Bearing On Anything, it all hangs together rather well.
As for the origin story, LoS is kind of a no-show on that, it pulls the Daredevil trick of showing you the character's origin minus the part where they actually got all their stuff; in this case, minus even the part where he actually becomes a vampire. So LoI more or less wins by default through actually having one, even though it's not a good one; seriously, Mathias would go from best friend to ruining Leon's life on purpose that fast?