Av is so slanted in the alliance's favor. I'm surprised that even a decade after the release of Alterac Valley we're still arguing over it.
Their entire side of the map bottle necks you into small areas that are easily manageable and allow their ranged classes to fire away without fear of being attacked back. Not to mention that their archers actually defend their flag and are consistently shooting.
After you get passed the stonehearth bunker bottleneck,you can pick one of 2 roads with limited movement and ever respawning npc patrols. If you make it all the way to stormpike graveyard and manage to take it,then you're left with the bridge. The bridge is the single easiest part of Alterac Valley to defend. A single mage with improved Blizzard has such a massive effect on the entire horde side. And while you're fighting the alliance on the bridge,their archers are merrily spamming you with arrows from the safety of their unreachable bunkers. Meanwhile,blizzard designed stormpike graveyard to be easily harassable by giving it cliffs that allow alliance to shoot at you when you spawn. And if you somehow manage to get inside the alliance base,you have both bunkers shooting at you and their tightly packed npcs aggroing like crazy while the few advantaged defenders have an easy time of picking you off.
I mean honestly. I played probably my 6th game of Alterac Valley,I don't see why alliance are so bothered by the back door. It's so easy to defend against. I saw about 10 horde stopped dead in their tracks by like 3 alliance.
Compare that to the horde side. There's 2 bottlenecks on the entire horde side of the map. Iceblood graveyard and the small ramp in the Frostwolf base(And even then that area has poor line of sight) leading to the base of the 2 towers. So once you break through Iceblood and take tower point,you're home free. The land is wide open and the npcs far and few. There are no cliffs to limit your range or allow the horde to shoot at you with impunity,and there isn't some gaping chasm that stops you from entering their base. In fact all you do to get inside the horde base is hop the wall(or ride right in),ride behind the huts,kill 1 or 2 elites tops. Then run into the towers whose archers wont shoot at you while you cap their flag. From their,most of their npcs are safely 100+ yards behind you and won't defend their graveyard like the alliance npcs do. The only advantage I can think that the horde have over the alliance is Drek'Thar's 2 easily killed wolves.
Basically this is what it's like to do AV against alliance that have half a mind to defend.
https://www.youtube.com/watch?v=Chzhf7gQxIg