Okay, sure. If we’re going to go down that road, we can. If we’re going to attribute all the possible in-game actions to every character, then yes, they did contribute to the burning.
They also saved the world from the Burning Legion. From three Old Gods. From an alternate timeline orc army. From Deathwing. From Garrosh and from Sylvanas. From Zovaal. The Horde adventurer helped save Nordrassil as well.
The Horde adventurer did help in the push through Ashenvale and Darkshore, that is true. But they did so under false pretenses; the Alliance, we were told, was planning a first strike and had spies in Orgrimmar to back that supposition. We were led to the beaches of Darkshore under the belief we would occupy Teldrassil to prevent an Alliance strike with Azerite McGuffins. We were clearly misled.
And as soon as a resistance against further atrocities occured, we became Schodinger’s Horde; both turning against Sylvanas and also still sinding with her. It was a very weird time, and I still feel like I’m in a superpositional state from all that.
But. On a more personal level for the all-encompassing Horde adventurer and their many deeds.
We’re clearly someone well-liked by Malfurion. In Hyjal and Val’sharah, he asks for our help without reservation. And the Horde adventurer is clearly fond of Malfurion as well because we always willingly give that help without a second’s thought. When we was captured by Xavius, who was it that braved Darkheart Thicket to rescue him? Yup, the omnipresent Horde Adventurer. Who braved the Emerald Nightmare with him? The Horde Adventurer.
And when Tyrande was ready to explode from Night Warrioring a little too hard, who was there for her? The Horde adventurer. When night elf souls were stuck in the Maw, was it Shandris who rescued them? Tyrande? No, it was the beacon of nobility and honor, the Horde adventurer. This same Horde adventurer who readily answered Tyrande’s call to save another world tree, as they did when her husband made a similar call in Cataclysm.
The Horde adventurer has saved Teldrassil by virtue of stopping the entire world from ending at least four times before they unwittingly assisted in Sylvanas’s atrocity.
I think it makes sense that Tyrande would want such a powerful, respected, beloved hero of Azeroth to feel comfortable around her and her people.
After all, it’s only a matter of time before she needs their aid once more, while Malfurion is like… Napping in Ardenweald or something.