It's an understatement to say that One Piece is an incredibly popular and immensely successful manga series for a myriad of accurate and legitimate reasons, but based on its lackluster start, there's no chance it would have survived in today's Shonen Jump.
With Shonen Jump's current model, budding manga series are put under immense pressure to perform well early on because if they fail to garner enough sales during this time, the manga anthology axes them by the seemingly arbitrarily chosen 19th chapter. It's, therefore, not uncommon for mangaka of brand-new series to expedite their plotline in an attempt to engage readers and amass enough of a following to stay serialized. In other words, there can't be many—if any—lulls in the story. And One Piece's early chapters are quite sluggish. Even the most fervent fans are aware of this failing and why there are numerous Reddit channels encouraging new readers to just buckle down and struggle through the first 60 or so chapters until they inevitably lose themselves within the massive world of One Piece.
Since the complexity of One Piece's heroes and the interconnectedness of its arcs have yet to develop, newcomers aren't shielded from the manga's many faults and shortcomings in the early chapters, most especially the two-dimensional villains and antagonists Luffy faces immediately. Although part of the series' charm is its childish comedy, the fact that every one of these early antagonists possesses the same over-the-top personality is tiring. Luffy's childlike wonder and unshakable focus on his dream might capture readers immediately, but it isn't enough to keep them there when such a compelling hero only interacts with foolish, bumbling idiots.
The sad part is that the first major battle occurs against the only one of Luffy's enemies at the time who had eaten the Devil Fruit—Buggy the Star Clown. This confrontation should therefore be momentous, except Buggy's ridiculousness drowns out his obvious importance. However, there are promising moments during this slog of a read foreshadowing the complexity that is to follow about 50 chapters later, like when the manga explores Buggy's early history with Luffy's hero "Red-Haired" Shanks. It would have been much more beneficial, however, if captain Kuro were the first of One Piece's long list of powerful villains, as he was a much more complicated character who, most importantly, didn't shout 24/7. Even more ironic is that one of the most random, unconnected story lines in the early chapters featured one of the best moments within the sea of dullness—it was even confined to one cell. It occurs during chapter 22 when Luffy meets the ridiculously rendered Gaimon who describes the perils of the Grand Line, illustrating the terrifying effects it has on even the strongest of pirates.
That said, probably the most outrageous failure of all was the complete absence of the ubiquitous debut chapter twist that is so critical in manga, especially today. The pilot of every new series is usually more than twice as long as the stereotypical installment to give the mangaka enough space to effectively set the stage of where their story will take place. During this crucial time, the mangaka not only introduces readers to this new world but ends up flipping it upside-down, shaking readers to their core even though they just learned about it. Nothing like that even remotely occurs in One Piece's premiere. Adding to the irony is how One Piece has become notorious for unexpected twists that even the shrewdest of fans can never seem to predict. These are only some of the many examples, proving that One Piece would have likely been axed by the time chapter 19 rolled out if it had debuted today in Shonen Jump—even though it would eventually become a masterpiece.