There is a 100% easy way to win Wintergrasp in very short time. All you need to do is, gather a raid 10-20 min before Wintergrasp starts.
If you’re defender
Move your defense as close as possible to the spawning place of the enemy faction and/or to the western/eastern Workshops. Once the Wintergrasp Battleground starts, catch as many horde as possible on their way to the keep. Hold the workshop as long as possible to prevent them from having many siege weapons.
But nothing really spectacular! The real exploits comes in, when you’re attacking the keep!
If you’re attacker
Have a warlock and 2 people fly to one of the towers. They need to be quickly to get inside the keep to one of the towers, before they get dismounted or detected. On the tower let the warlock place a summoning stone.
Now port your whole raid to the tower and hide. Make sure they are staying somewhere on the outer lines where the gun spawns, so they don’t get ported out of the keep when the siege begins.
When the siege begins, you won’t be ported out of the Keep. Now simply wait until your enemy enters the outer yard, charge out of the tower and roll over the allies. You will get the necessary kills pretty fast for First Lieutenant. Who ever dies in the keep simply gets a Wintergrasp Demolisher or Siege Engine. And wait in front of it. Once your faction got 16 vehicles, zerg down the walls and go for the artifact room. Zerg it too and go in and win.
I guarantee you, your enemy will be surprised as hell and you will have easy game rolling over them. The main advantage of this exploit tactic is, that you can destroy the guns from within and don’t have LoS problems or allies who shot from above the small gun terraces (and if you’re melee you can get up there anyways) and of course very quickly gain your rank for the siege engines!
Have fun owning Alliance/Horde with this dirty tactic!