First of all, I'm pretty sure people can react much faster than 6-7 frames. Example: Smash DI.
Second of all, even if you were absurdly slow to react, the hit lag and shield stun alone will already add up to more than 7 frames. A 3% attack gives you 3 frames after hit lag AFTER the move connects and keeps you stunned in your shield for 7 frames. That's 10 frames you have AFTER the move hits to react. Not to mention the fact that the move doesn't hit on frame 1, so that also buys you a bit of time. On top of that, you can act 5 frames before him. So you have around 15 frames to decide to start a grab after the jab hits. If you opt to Fortress, you have all the frames before the grab actually comes out too (pretty sure that'll be either 6 or 7 frames, too lazy to look.) So 20+ frames in the case of the Fortress.
Third of all, it's not like Falcon teleports in front of you and jabs. You see him coming. If you're holding shield you're not distracted with your own actions, you're looking at him. You not only have visual cues telling you "Hey! He hit your shield. Grab him now", you also have sound cues too.
There is really no excuse. A bit of buffer will practically guarantee success.No it doesn't. Your opponent's not going anywhere in 1 frame. If you were gonna hit him with a 1 frame shine, you sure as hell will hit him with a 2 frame shine.