I wouldn't know, I was being camped in a tower the whole time, outnumbered on both sides of it if we tried to push out.
I agree it's pretty easy to get on the walls, but if it was 1:1 the attackers would at least have to fight on the walls man to man against faster spawning defenders, which would mean heavy casualties. Instead they only lost 900 tickets, taking a 2500 population castle, ending it with a flag win near the end.
It's not that there's no mercs enthusiams, lots of people would sign up for D, it's great xp. You what seems to be the equivalent of a 5x for an hour, but with no gear upkeep costs. But if someone signs up, is accepted, and doesn't show, it fucks over the whole system. That's why there needs to be harsh penalties for that, to discourage it or it completely unbalances strat and invites cheating too (getting friends to sign up for NPC defence, who never intend to show up).