There’s some misunderstanding/conflation going on here.
The Horde champion did no such thing. They and Saurfang fought their way to Dark Shore under the assumption that the goal was to occupy Teldrassil. Sylvanas decided she wanted to torch Teldrassil and the actual launching of the catapults was performed by NPCs.
So the Horde champion will have to deal with the weight of not immediately doing everything in their power to stop it and Sylvanas right then and there, and not holding their fellow soldiers accountable, but acting like they gave and executed the order because you can’t get your hands on Sylvanas or some random NPCs is just using them as a scapegoat.