I'd agree with Solo. IMO Fox is nothing special in terms of punishing shields.
Honestly the the most consistent thing aside from just grabbing (for me anyway) is spamming jab/drill on their shield until it pokes. Position yourself with the drill so you can land behind them and they can't shield grab.
That's not 100% reliable either though and will get punished by certain chars. Falcon can upsmash, Pika can nair, Fox can shine, etc.
Correct me if I'm wrong.
The quote from firo is as follows: "With a hit on an opposing character's shield, fox should be getting a high percentage combo, or a kill, almost every time."
I don't think that this directly mentions shield poke in the first place but I'll get to that. I think that the point made is that a "20XX" Fox would be able to break an opponents shield at the drop of a hat and follow up with a solid combo. Isn't perfect shine pressure on shield 100% inescapable? If it was inescapable, I could see a few scenarios where the setup for shine pressure would result in failure but that percentage is fairly low.
As for Fox's superior shield poke game, I think he is better than the majority of the cast at shield poking -> combo
This list assumes that the opposing players are on a completely solid, flat part of the stage:
Falcon- good at shield pressure but his shield pokes are sub par
Samus- virtually only a shield pressure game. Samus has bad shield poking tools, iirc (forward tilt isn't a combo starter)
Yoshi- good shield pressure/poke game all around. I think he beats most of the cast in that regard (
Pika- down tilt is nice but it doesn't lead into a combo very often. up tilt is only useful on a small shield and pika's shield pressure seems to be lacking to me. she often can't reduce the shields size enough before an up tilt but I could be wrong
Mario- fireballs allow him to close in and his down air is nice shield pressure and leads into shield poke sometimes. He's average
Luigi- unlike his counterpart, Luigi's shield pressure suffers due to his fall speed. His down air should be adequate but it lacks the utility that Mario's down air has.
DK- worst shield pressure game on flat ground? only has down tilt for pokes and that doesn't lead into anything
Puff- decent shield pressure with down air and has a good up tilt. average
Link- down tilt is almost too slow so it's hard for me to speculate. boomerang is nice but it has drawbacks. grab is too slow 75% of the time for shield pressure and it doesn't combo. up tilt is arguably his best option and it doesn't poke well.
Ness- good shield pressure but his DJC tricks are only good at the right staleness, iirc... I'd place him at third
Kirby- nice up tilt but the knockback on shield is high, iirc. Down air is amazing
Fox- IMO he's the second best at shield pressure/pokes, just below Yoshi. Down tilt is fantastic. his drill is solid. up tilt is nice. shine pressure has potential. His fall speed is helpful on shield. fair/bair have low enough knockback to keep the enemy close for more shield pressure and a potential shield poke
My shield pressure/poke character list on flat ground:
1. Yoshi/Fox
3. Ness
4. Kirby
5. Mario
6. Falcon <- only because of his grab, otherwise he'd be near the bottom
7. Puff
8. Samus
9. Luigi
10. DK
If any of this is misinformed or just ignorant, please tell me.