The Sunwell event took place over 12 years ago, but it doesn’t really mean that their race hasn’t all overcome their addiction. Granted, the BC starting zones haven’t been updated their stories.
Okay now were comparing apples to oranges. Let me explain:
The demon blood was meant to act as a drug; to whip them into a frenzy and enhance the Orcs abilities. When they were cut off from that source: clan warlocks, they descended into a lethargic state.
The ones who drank demon blood were never addicted to fel magic but were bound by it, spiritually and physically. Again Blizzard has never gone into depths about why but I’d estimate that it’s similar to taking performance enhancers and then not having access to it.
During WC3, they also meet that physically link in Mannoroth, who after being killed by Grom, freed themselves of that link.
And finally, you didn’t state that Highborne were Nightelves, you said: “As for the Highborne, all elves were Highborne until the sundering”
There was only one race of elves during that time period: Night Elves.
Highborne was a society of Night Elves; primarily Magic users. i.e. Azshara, Xavius, Vashj, Illidan, High Elf/Blood Elf ancestors