I think it was just Jack doggedly searching for them in the general area of the sea he had last found them in until he got lucky. I doubt theres any more conspiracy than that.
I'm (almost) astounded that anyone thinks Jack has been permanently defeated or has been de-hyped significantly. The Zunisha defeat was a brilliant plot move, akin to the Knock-Up Stream that saved the Straw-Hats from a premature battle with the Blackbeard Pirates.
Whats-his-name with the green text is trippin over that monkey falling thing too. What with the "you'd think he'd better be better at balancing and staying calm if he was the lookout" stuff. Ever read One Piece? Him falling at the beginning was definitely plot convenience, but Oda has now book-ended the arc in a funny way with his two falls.
I agree with everyone who has been saying that Luffy was likely not "stronger" than many of his key Pre-Time Skip foes.
If Crocodile had taken Luffy more seriously he could've easily defeated him in the beginning, but due to Luffy's luck, skill, and persistence, the physical power-house that Luffy has always been was enough to defeat a haggard and (most likely) increasingly desperate Crocodile. Give those two a fresh re-match anytime before Gear 2nd and I think Crocodile would've had a very decent chance of defeating him.
Enel clearly was 50 times stronger than anyone around, but due to Luffy's luck, all of his really powerful attacks were worthless and Luffy could defeat him bhy forcing Enel to fight in a way that didn't suit his true strengths, relying soley on Mantra and physical combat.
I think Luffy really does equal Lucci entirely and squarely after he discovers the Gears. That said, I think both Crocodile and Enel would be able to take Lucci due to his aparent lack of Haki (at the time). If Lucci had had Haki he would've wiped the floor with Croc, due to speed, but I think Enel might've still beaten him with his devestating elemental projectiles and ability to move lightning-fast. Just a thought though.
Moria was certainly weaker than Luffy, but like many more minor villains, just had a bizarre fruit that gave Luffy a lot of trouble. With shadows, I think Moria would likely have been defeated by Lucci, Enel, or Crocodile had any of those fights gone down.
This is part of the fun of the rock-paper-scissors nature of One Piece battles. The match-ups always matter a lot.
It seems to me that a lot of One Piece fans have a "everyone is a Saiyan" mindset where with every battle they become significantly stronger, when really I think they grow mentally much more than anything. Because of this mentality a lot of people would assume that the order foes appear in has a LOT to do with who is stronger. Like, to me, nothing suggests that say like, Arlong wouldn't probably kick Bellamy's ass. Arlong was only a little weaker than Luffy phsyically and Bellamy was clearly WAY weaker, and all Luffy did between those two fights was punch peopple for a few weeks.
And to bring that tangent back to the relevant topic: Jack is still a threat. Luffy will most-likely deliver a final blow to Kaidou and in no way will that suggest that Luffy is suddenly as strong as Kaidou at that moment. And it wont mean that everyone he defeats after that is necessarily "stronger" than Kaidou. What really seems to ramp up steadily from arc to arc are the tough circumstances, and I have no doubt that big battles in the future will all be increasingly tough struggles for our heroes, and none of it will mean anything if you just apply DBZ/shounen logic. One Piece is certainly in the shounen genre, but its the best of the best for a reason.