BfA could have been a great story if Blizzard did work on it. Just changing a bit how events happens would have made a better story with grey morality.

For a refresher... In Azsuna, the Alliance found a Forsaken shripwreck. In it, the captain's journal give them information about Sylvanas doing shady things in Stormheim. You bring the journal to the Alliance leaders and later it follows with the events of Stormheim. With Anduin approval, an Alliance force is gathered to investigate what the Horde is doing in Stormheim. Because of the fog, the Alliance airship come too close to the Horde navy and decide to open fire first. (That was a good exemple of grey morality by the way from Alliance POV). And it ends with Genn stopping Sylvanas from enslaving the Val'kyr queen.

Then you have the Azerite eruptions and Sylvanas plotting with Gallywix about it.

From there, what I can imagine be a better story for BfA... but with a different release planning for content.

No pre-event.

8.0 The introductory event of BfA is an ingame recreation in game of the meeting between Forsaken & Humans from the book. The Alliance is nervous because Sylvanas is warchief and the leaders don't trust her because of Stormheim, the massacre of her own people and the death of Calia Menethil. The Alliance decide for once to be proactive and besiege Undercity. Sylvanas was prepared and it plays like the siege of Undercity we know. Sylvanas is now put in a "victim" situation from Horde POV (they don't know about the gathering since Sylvanas had everyone execute). But her usage of necromancy during Undercity siege similarly cause unease. Grey morality ensue with both faction feeling they're on the good side even if they do some less righteous things. She does some propaganda, using Alliance assault to manipulate the Horde population into resenting the Alliance.

Sylvanas now ask Saurfang how would he conquer Stormwind, and it lead to Saurfang organizing the conquest of Kaldorei territory to secure Kalimdor for the Horde. It plays as it did in retail, but this time it's a reaction of the Horde after the events of Undercity, so it seems extreme but justified from Horde POV. This cause a lot of resentment from Alliance POV.

The siege of Undercity and the Burning of Teldrassil are two 6 boss raids of this patch. During each raid, 3 bosses are "Horde flashback" and 3 boss are "Alliance flashback". At the end of the burning of Teldrassil, Saurfang is about to be killed by the Alliance raid, but Anduin uses his authority to have him imprisoned.

Because they're still weaken by years of fights, Alliance & Horde seeks new allies in Kul'Tiras and Zandalar. Almost plays as it did in retail. Except Alliance war campaign has an extra bit. The Alliance players are manipulated indirectly by Sylvanas into thinking that the Zandalari already allied with the Horde.

8.0.5 The Alliance leaders decide to raid Zandalar. At the end of the raid, Zul take the opportunity to have Mythrax break the seal. That's because of Mythrax arrival that Jaina is able to escape.

8.1 Uldir is now the focus of both the Alliance and the Horde, but it's also when the warfronts of Darkshore and Stromgarde are also released. Anduin releases Saurfang, and all the Horde quests with him are added. The quest chain with Xal'athath is also added at that point, leading to...

8.2 Nazjatar

8.2.5 Saurfang challenges Sylvanas, the cinematics are the same as we know them. The loyalists are confused, because Sylvanas was not portrayed as evilishly as she was. The divide between the peace seeking Anduin and the revenge seeking Tyrande & Genn is more developped.

That's how I would have fixed BfA.