You can use thrust asymmetry to help with yaw, yes.

But here we're talking about unplanned sudden thrust asymmetry, causing a massive yaw force at a critical phase of flight, takeoff, where you're engines are likely to be near their full power and you're close to/on the ground.

If you go from 8 engines to 4, loosing one engine goes from causing 25% thrust loss on the wing to 50%.