In One Piece, there are many instances where the hero's victory feels well deserved. For example, Luffy might obtain a monumental power-up to secure the Straw Hats' victory or make a decision earlier in the narrative which happened to have a massive pay-off.
However, it is just as common for the Straw Hat Pirates to be saved by plot armor. Many villains proved superior to Luffy in every way, only losing on account of his narrative significance and fictional tropes.
10 Arlong Had A Home Field Advantage
While far from the strongest villain in the series, Arlong still ruled the East Blue with an iron fist. Capable of catching cannonballs and shattering them in his mouth, he was physically superior to Luffy in every way.
To make matters worse, Usopp had virtually no experience during their foray into the park, and Zoro was already injured. Arlong also had the advantage of a nearby ocean, meaning that he easily could have drowned Luffy if he actually committed himself to it.
9 Aokiji Let The Heroes Off The Hook
Aokiji first appeared at the end of the Long Island arc, easily defeating all the Straw Hats. He had a perfect opportunity to kill or capture them but instead let them off with a warning.
While Aokiji's mercy may have been to repay an old favor, it was also oddly convenient since none of the Straw Hats had the strength to oppose him at the time. He could have also captured Robin at the end of the Enies Lobby arc though chose to talk with her. Aokiji was much too powerful to be introduced so early in the series.
8 Magellan Realistically Should Have Killed Luffy
As the tyrannical warden of Impel Down, Magellan was one of the first villains to meaningfully punish Luffy's recklessness. A single drop of his venom proved sufficient to hospitalize an average person, and Magellan forced him to bathe in it.
After finishing up, Magellan banished Luffy to Impel Down's frozen prison to waste away. However, Bon Clay conveniently happened to locate and deliver him to Ivankov. Considering the incredible circumstances leading to Luffy's survival alone, they never should have been able to escape the undersea prison.
7 Crocodile Wasted Two Perfect Opportunities To Finish Luffy Off
Crocodile was the first villain to defeat Luffy twice. The first victory was a complete humiliation, as his opponent had no idea how to counter his logia-based Devil Fruit.
Instead of killing him, Crocodile left him to rot in Alabasta's blistering dunes. He spared him again during the attack on the capital, presuming that draining the young hero of water had finished him off. Considering that it took three complete matches for Luffy to finally prevail, Crocodile deserved his win much more than his opponent did.
6 Lucci's Organization Had The Perfect Chance To Defeat The Straw Hats
Rob Lucci and the CP9 agents had every conceivable advantage over Luffy. They gained the trust of Water Seven, divided the Straw Hats, and were physically superior by a large margin. Lucci himself even defeated the heroes in advance, only sparing them so that he'd have a target to frame for his crimes.
When attacking Enies Lobby, Luffy conveniently discovered two entire Gears in order to bring Robin back home. Considering his dramatic growth in such a short amount of time, Robin realistically never should have been saved from her fate beyond the gates of justice.
5 Kaido Had A Bad Habit Of Sparing His Enemies
If Kaido weren't completely horrible about letting his enemies live, they never would have been able to thwart him at Onigashima. He didn't care when the Scabbards returned, spared both Luffy and Kid to work in Udon's pits, and even let Trafalgar Law slip through his fingers.
All three men proved instrumental when defeating him and Big Mom, two powerful fighters no one else would have stood a chance against. If Kaido didn't get so overconfident after his first victory against Luffy, he might have executed them quickly like he did with Oden. Some may argue that he spared them deliberately so that he'd receive the glorious death he wanted.
4 Jack Had Technology & Intelligence Over The Minks
Jack was an enormously powerful pirate sent to attack Zou and retrieve Raizo. Although the Minks fought tirelessly to defeat him in shifts, he had many advantages that realistically should have guaranteed a victory.
In addition to having the element of surprise, Caesar's bio weapons were more than enough to debilitate enemy forces, leaving them sickly and weak. Kanjuro had also been feeding Jack information the entire time, which meant that he knew exactly how his opponents were going to react within a matter of a few hours.
3 Gecko Moria Had The Sun On His Side
Despite being the weakest warlord, Gecko Moria could have defeated the Straw Hats if he fought smarter. Since he managed to extract most of their shadows, all he needed to do was hide until the sunlight finished them off.
Granted, Luffy gave him a tough chase, forcing him directly into the arms of his giant, Oars. However. if Moria simply fought to buy himself time rather than win, he could have waited out Luffy's shadow enhancement and secured a safe victory.
2 Kizaru Nearly Wiped Out Everyone At Sabaody
When Kizaru attacked Sabaody, the results were devastating. Despite being outnumbered by the Straw Hat Pirates and the entire Worst Generation, his marines had them on the run in a matter of minutes.
Although doing his best, Rayleigh could only buy the heroes time to escape. Should Sentomaru have caught up with them before Kuma, the Straw Hats never would have been able to survive. Kuma's positioning is one of sheer convenience, as the marines could have requested any other warlord aside from Hancock to help in his stead.
1 Blackbeard Should Have Massacred Marineford
After stealing the Tremor-Tremor Fruit, Blackbeard became the single most powerful person at Marineford. With the Whitebeard Pirates demoralized and the marines badly weakened, he was in a great position to defeat Sengoku and bathe in the blood of his enemies.
The only reason Blackbeard stopped was because Shanks conveniently showed up. Were it not for the deus ex machina in the form of the Red Hair Pirates, Blackbeard and his forces would have had no trouble crushing both parties and making the once-great naval base the foundation for their new villainous empire.