Being able to lock flags becomes meaningless when your team can't win a group fight.
I played a random game yesterday, Oculus/Oculus/Erebus vs. TB/Oak/Sedna
It didn't matter that my team had only one stun and no interrupts against a stun, three interrupts, and silence because double oculus does so much burst damage to everyone the sedna didn't have time to heal, and oak could only save one person. Locking is just really annoying, but if you're on your A game, people won't be able to capture your portal flags in the first place.