Actually not. My handguard saw will do as well as the sawstop non-destructively (independently tested and verified, so you don't have to take their word for it).

They do it (basically) by predicting whether your hand will touch the blade, rather than waiting until it does touch the blade.

If you wait until someone actually touches the blade, then yes, you have to operate very very fast. That is unavoidable due to physics, as you say.

But if you can gain 100ms or 250ms by proving a 100% probability that the hand will touch the blade before the person can stop it, you now have a lot more time to stop the blade.

The blade doesn't have to stop. Some saws have the entire blade assembly lower. If you walk the table saws at AWFS you'll see all types of different safety systems.