Bfa was her "full descent" the problem is how it made no sense, because everyone was backing her maddening for no reason, and was a straight up copy of MOP
things would be handled better if she, in the shadows(not as warchief), was dealing with "unknown powers" to reach immortality.
Hell, they could have used this as a link to the Janitor so we care about him:
- In Legion, Sylvanas, in the shados(meaning, no one else knows) is searching for a way to get eternal life trought necromancy, she seek Helya, who teach how to see the Shadowlands like Odyn did (that explains the deal.)
- Sylvanus gouge her eye out and scout the shadowlands, she find a primordial entity of death trapped, they make contact and a pact is made, his freedom for eternal life and absurd power.
- At the end of Legion Sylvinas abandon the forsaken(now leaded by the council,) to free the Janitor, we don't see her in the entire BFA expansion
- She succeed in breaking his chains, they both fuck up the arbiter and they start messing up with the shadowlands, now the covenants have a problem, some of then sided with the Janitor.
- The Lich King sense something is fucked up in the shadowlands, he ask the aid of alliance and horde
- The war didn't stop in bfa, but they have to make a truce, cause people dying are fuelling the Janitor power(so, now it makes sense of why only one war of a small planet could be so relevant compared to the multiple planets we have).
- Then we seek the lich king to go there, then, we have an expansion there more compelling with more "palpable" reasons to fight for it..
Don't want to sound hubris but this feels much more organic and logical to me.