While this is true, I've seen QB's fake that move and sucker a defender. Until it's illegal for the QB to fake going down or out of bounds, I can't really blame the defender.
I can agree there can be plays in the gray area but Lawrence clearly went into a sliding motion four yards away from Al-Shaair.
I think they refined the slide rule to reduce the need for the defender to hit the QB. The rule is triggered as soon as the QB begins the slide - he’s down as soon as his any part of his body not his feet touch the ground.