The Horde still possibly still has Ashenvale, or at least parts of Ashenvale - they still need resources, or else they can't realistically survive, and Ashenvale still has plenty of those. They likely pushed towards Stonetalon Mountains, Feralas and Desolace as well during the conflict. As the night elves gathered most of their soldiers from their outposts, it is likely they abandoned most of their other bases after Teldrassil was destroyed. Tyrande was willing to concede Azshara after their last war despite everything the Horde did to her people, so it's possible the night elves have conceded some lands this time around as well.
And I doubt most of the Horde population would have allowed the Horde Council to agree to unfair negotiations, they would have been torn apart otherwise. The Forsaken raised lots and lots of humans - and other people - from the dead, in fact, I'm surprised the Horde was losing the war, giving that Sylvanas could raise hundreds or thousands of her own people from the grave, as well as her enemies apparently.
Remember, in the original cinematic, they showed both factions almost entirely controlling each continent. The night elves might have Darkshore and Nordrassil - but the Horde very likely still controls most of their continent.
Perhaps. But we don't know their exact capabilities, they have flying machines, but does it have any kind of major game-changing offensive weaponry? If you're so passionate and knowledgeable about the lore, then perhaps you and others should consider contributing to Wowpedia, some of their articles are probably a bit incomplete and outdated.