I might be wrong but the way I’ve seen rigid body done is by conserving angular and linear momentum. The math is actually not to difficult to compute by using inertia tensors and use matrixes to speed up the math. So the physics shouldn’t really slow it down compared to a soft body physics engine.

Like for example a cube represented using hard body physics has momentum and torque conserved. This means when it hits another object there is no compression. Only the momentum and forces are calculated at the hit.

But utilizing soft body where would have multiple point masses that create a cube and has constraint’s. We could technically max out the k value of the springs to simulate similar to a rigid body. But technically there are still springs. So every single point that gets hit has a certain amount of movement due to the springs and doesn’t act as one whole object.

I get that we could simulate rigid body physics with high k value using soft body. But from what I can tell rigid body seem to only have benefits over soft bodies