I read nice reasonings for defending in middle.
In theory it should work, then why in pugs almost everytime half team that playes middle has a loss?
Because enemy fc is escorted by healers and reaches their base and who knows why those in middle don't think about following them inside. (score dmg epeen syndrome?)
When they wake up it's too late, their fc with 7 stacks got oneshotted by random stealthers / those that didn't cross middle, but cleverly reached base running from the sides (facepalm).
So in pugs by experience, the best defense is to move in a big group with a healer and nuke the efc on sight, no matter where and leave brain-required strategy for premades.
In other words an aggressive stance in the best defense.