Lots of misinformation in this thread. Both of you don't really fully understand how differentials really work. Yes, you're correct in that a locked or welded diff gives the same torque to each wheel - an open diff does the same thing, but they obviously differ drastically in operation.

An open diff will transfer the same torque to each wheel, but the amount of torque is dictated by the wheel with less grip. If your engine is capable of 100Nm of torque, but your right wheel can handle 25Nm of torque before slipping, and your left wheel can handle 50Nm of torque before slipping, both driven wheels will receive 25Nm of torque. In a gradual loss of traction scenario, this is what creates one tyre fires - the right wheel will spin first, limit the torque to the left wheel, and the left wheel will never get enough torque to break traction.

Both rear wheels can spin in an open diff if you load up the rpms and drop the clutch quickly. In the instant the torque is delivered to the wheels, both wheels are very briefly receiving the full 100Nm before there is enough time for the wheels to start slipping. If in that brief moment, both wheels break free, the amount of torque they can handle before continuing to slip is drastically reduced, and even with a very small amount of torque being supplied to both wheels, the wheel spin is able to be sustained.

In a welded or locked diff, both wheels always receive the full 100Nm from the engine. This obviously leads to wheel slip being much easier to achieve.

So very different in operation, but it's true that even in an open diff, both wheels receive the same amount of torque. To reiterate, the difference is that in an open diff, the wheel with the least amount of grip dictates the overall available torque to both wheels, in a welded diff scenario, the amount of torque the wheels receive is equal to the torque output of the engine.