No. It is not the drawing of life which creates fel. It says right there… it FUELS fel, life force is USED to produce fel… but the act of drawing life force IS NOT fel.
I see what you’re getting at but I think you’re downplaying the wording when it comes to the drawing of life - fel magic is fueled by drawing life from living things, but both the drawing of that life and its use is fel. Hence why the warlock draining someone’s life constitutes a fel spell. You could also look at is the warlock immediately using that life as fuel to empower himself, which is the fel portion, which is also a viable reading.
The act of siphoning an essence from living beings can be described as vampiric, yes.
Yes, and drawing the essence of a living being, especially a thing like say a mana wyrm, a fellow elf or a demon, which are sustained by magic and using that mana to feed yourself means that in that context, the drawing of mana and life overlap. Hence it being a fel spell. The same would not apply if you drew from an untainted object and the high elves have no issue with that. Which ended up biting those guys in the lodge when they overindulged and became wretched, but that’s another topic entirely.
You are right that Kael had mana drain as well as banish before he met Illidan and this in general is more of a grey area. In terms of WC3, the new source that Illidan promises him and the blood elves is explicitly demons, it being draining from any kind of thing is only a later change. The most recent source is Chronicle Vol 3, the page in the version I’ve got is 133, but this might vary, the chapter is called Burdens of Leadership and it has Illidan as the one to teach Kael and company to drain mana not just from living things but from items and the environment. The earlier WoW encyclopedia version is a bit more vague since there it’s just mentioned he taught them about draining alternate sources and both would be contradictory since it’s also mentioned that Kael already knew how to drain mana from the leylines, ergo the environment, and did so with Dalaran, it just wasn’t enough. We also see that the Nightborne knew how to drain mana from the environment and items just fine with their siphons, so this whole thing is a bit of a mess.
The main thing that’s consistent though is that they didn’t know how to drain mana from living things, despite Kael being one of the Council of Six and Rommath being capable enough to be Grand Magister until Illidan taught them that, and that the things the majority drained had mana and life be the same thing, like with mana wyrms, so the draining of their lives to buff themselves, taught by a demon and unknown to the top mages of the time otherwise is a form of demonic magic. The only version that contradicts this and has Kael already know how to is WC3, but new lore trumps old and even if it didn’t, the WC3 Blood Mage Blurb makes clear that all of those were demon magic:
Calling themselves ‘Blood Elves’ - these cold hearted refugees seek to expand their remaining magical powers at any cost - even if it means courting the infernal powers of the Burning Legion!
clas sic .battle.net/war3/human/units/bloodmage.shtml
Mana Burn is used by demon hunters, but like you mention it’s also used by priest and it isn’t actually a draining spell, so I left it out of my examples on purpose. Mana Burn for priests comes from a simpler time where all this was a lot more unclear. In current lore I can see how fel can be used to blow up mana, since it’s adding disorder to order, I can see how you could move arcane from one to another, but I’ll freely admit I don’t get how you’d go about using Light or Void to achieve the same.
P.S: I can’t link Blizzard’s own sites because the word for 
is in the filter. Good job, Ion.
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