Varian succeeded in bringing the blood elves back into the alliance.
Putting aside that garrosh's biggest win (theramore) was thanks to BE technology, think about it- BEs join the Alliance. Sylvanas is already scared of the Alliance attacking the Forsaken in tides of war, and now she loses her only ally in the region. Horde loses lordaeron, Horde loses Quel'thalas, EK becomes Alliance territory. this is really bad for Garrosh- he has only one front to fight on now, and the alliance no longer has to worry about the EK.
With the BEs back, they get Dalaran back anyway after Varian tells Lor'themar to weed out the sunreavers responsible for theramore (instead of jaina going apeshit). the tauren and trolls would probably follow Lor'themar's example, to be honest, since they HATE garrosh, if the horde lost EK.. so what else does garrosh have? Org? Alliance forces attack from EK (sin'dorei and dalaran included), night elves from ashenvale, and garrosh gets stomped. war over.
Imo jaina screwed up bigtime. she could have won the war for the alliance in one stroke if she didn't attack the blood elves people and push them back to Horde, every logical outcome points the Alliance steamrolling Garrosh on their own if they succeeded in the EK. Its a domino effect- Anasterian destroyed the Alliance of Lordaeron when he left after the second war. Lor'themar would have set off the biggest win for the Alliance ever if he joined it.