You're missing what the actual rules for displacement are.
"Being displaced by your opponent" means "Pretend the opponent is a titan who has just landed on top of you".
In that situation, the rules specify that the model *being discplaced* chooses where it goes. Not the titan.
I know that it seems like RRG are making it deliberately confusing when they write the rules like that. But it's true. An attacker displacing a defender is a good thing for the defender. And a defender displacing an attacker is a good thing for the attacker. Because the displacee is the one in control.