I would definitely retcon it, or at least rewrite it. As so many people have said, the current story of the Burning has made deescalation of the war nearly impossible - at least without angering a chunk of the playerbase.
I had one rewrite idea rattling around from when everyone was speculating on how to start the war while letting both sides feel justified:
First, have Lordaeron come first. As I would write it, it would start with the Alliance hearing that the Horde has started building a port in Gilneas to more easily receive Azerite shipments from Silithus.
Genn immediately launches a reclamation effort, with support (including specific named characters) from most other Alliance factions, despite Anduin’s quiet disapproval - and the attack goes surprisingly well, since the Horde has most of its forces in Orgrimmar preparing to counter the night elf fleet moving to Silithus.
During the attack, the player finds notes on a Forsaken apothecary and goblin engineer showing the plans for a nearly-completed Azerite war machine. Genn is convinced that the Horde will use this to attack the Alliance as soon as it is finished (Jaina can have flashbacks to the mana bomb), and they attack Undercity to destroy it and prevent the Horde from using Azerite.
Cue the Battle for Lordaeron, with the Horde being the barely-prepared defenders while the Alliance shouts that the Horde are too evil/stupid/monstrous be trusted with this new superweapon, and must therefore turn over all samples to the Alliance for safekeeping.
Afterwards, however, the Horde player learns that the Azerite machine in Lordaeron was a prototype, and a finished model had just been shipped to Orgrimmar to join the Silithus attack. Sylvanas decides to divert this army and destroy the Alliance’s Azerite port both as retaliation and to keep the Azerite stockpiles from tilting in the Alliance’s favor.
I would change the War of Thorns to be a much more one-sided war, with the night elves using guerilla tactics to slow the march rather than trying to face the Horde war machine head-on. More spooky ambusher/woodland ghost thematics for the night elves, and more unstoppable charge moments for the Horde - when they manage to pin their opponents down, that is.
That frustration of not getting a fight would lead in to Sylvanas’ decision to burn the tree: She needs to destroy the harbor, but she doesn’t expect the whole tree to go up like a tinderbox (it’s a living tree in the ocean!) and just wants to give the defenders the right motivation to finally leave the cover of the forest and fight the Horde army head-on.
Then some unexpected shenanigans happen between using the Azerite war machine (which has a nice magical range upgrade over normal siege weapons), the Azerite stockpiled in Ru’theran, and/or the (explosive and flammable) Azerite sucked up by Teldrassil’s roots - and kaboom! The whole tree’s on fire. No backing down from total war after that. (or at least until Azshara appears.)
There’s a lot of details and tweaks that could be added, but I think that would have been a much better way to motivate both factions for the war without making the Horde irredeemably evil.