Yes, this is pretty much spot on. Accuracy isn't actually important, because in a theoretical mission where we're saving earth, well, it was already going to hit. We can't accidentally make it double hit, so the only thing that matters is changing the orbit enough so it no longer hits. And because asteroids are inert, it doesn't even matter if the new course isn't perfectly safe and would still hit earth next time it comes around, because when we know of an asteroid we can track it, so that case would buy sufficient time to do another deflection mission.