AV is so simple.
If not enough people defend and the enemy back caps a tower or two, you lose. Simply because the boss now has too much hp to be reliably rushed down.
You can still win if enough reach the other side and you’ve taken at least two towers/bunkers, I’ve seen both sides rush the boss down.
It all comes down to whether or not enough players are willing to slow the other team down.
People can’t be afraid to throw their virtual lives away in PvP. Good PvP’ers know that a dead person who capped a flag is better than a living person doing nothing.
Too many times I see players running around on their mounts, see combat, only to ride away. They could be defending, or help taking a graveyard (not Snowfall, nobody takes Snowfall unless they want to lose!)
Riding around while the other team does objectives is a surefire way to lose, and my belief that most teams that lose simply have more mounted players riding around instead of contributing.
This goes for pretty much all Epic Bgs.