The idea is that if the target is in motion when the LOS check is made, and they are in the clear, then it's a hit. Stun and drag em over. If the target breaks LoS while the hook is in flight, no go. Once you're hooked, though, you're stunned; can't just duck out of sight.
All they did was shift the LOS check's base from the hook itself to Roadhog, meaning you can't just corner poke anymore. You're a tank; go get punched in the face.