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At the beginning of One Piece, the three great powers that kept the world in balance were the Emperors, the Warlords, and the Admirals. With only the latter group being loyal to the World Government, it was immediately clear that these top-tier fighters were on a completely different level power-wise, and nearly every appearance from members of this elite rank has demonstrated this clearly.
However, looking at every Marine Admiral, past and present, it becomes equally clear that even they are not all on the level tier in terms of strength. While characters like Sakazuki and Kuzan stand among the strongest combatants in all of One Piece, others would be lucky to defeat Commanders like Marco, Katakuri, and King.
Former Admiral Zephyr Embarrassingly Lost to Luffy
While created by Eiichiro Oda, former Admiral Zephyr is a non-canon movie villain. And, by virtue of being the main antagonist of a One Piece film, specifically One Piece Film: Z, Zephyr has the distinction of being the only Admiral-level character to ever lose a fight to Monkey D. Luffy.
Throughout Film Z, Zephyr is presented as a true powerhouse, keeping up during his fight against Kizaru, who he'd previously mentored. However, it's also established that he isn't in his prime anymore, which is why he's ultimately able to be defeated by a version of Luffy who, at this point in the story, wouldn't have even been able to defeat Charlotte Katakuri.
Admiral Ryokugyo Has Failed to Impress in All of His Fights
Conscripted by the Marines as a replacement for Akainu, Ryokugyo has thoroughly failed to live up to his predecessor's reputation. To date, he's been a part of two major fights and, in both encounters, the eater of the Mori Mori no Mi has been the combatant to come out looking worse.
On Wano, the Admiral also known as Aramaki only managed to defeat King and Queen, who'd already been heavily injured and beaten by Zoro and Sanji, while Luffy trusted Yamato and Momonoskue to handle him, and he was ultimately scared off by the presence of Shanks' Haki. Meanwhile, during the Reverie, he couldn't even defeat Morley, a member of the Revolutionary Army presumably weaker than Sabo, Kuma, and Ivankov.
Admiral Fujitora Has One of the Strongest Paramecia Devil Fruits
Issho Fujitora is unique in that he's both the only Admiral to be a true swordsman, and the only one with a Paramecia-type Devil Fruit. Despite One Piece, as a series, having been taken over by Logia and Mythical and Ancient Zoan-type Devil Fruits, Fujitora's enhanced senses and mastery over gravity still allow him to stand among the best of the best.
Sadly, Fujitora has been kept out of the action since the Dressrosa Arc, a storyline in which he could have easily defeated everyone else present had he wanted to do so. As things stand, all that's clear about Fujitora's strength is that he's been presented with more gravitas than Aramaki, but that he's definitively weaker than both Sakazuki and the world's strongest swordsman, Dracule Mihawk.
Admiral Kizaru Defeated Gear 5 Luffy During the Egghead Arc
When the fight between Monkey D. Luffy and Admiral Kizaru began in the middle of the Egghead Arc, fans were ready to see the series' hero use the same power he used to defeat Kaido against the man who'd brought about the destruction of him and his crew two years earlier. These same fans were thus shocked when, in a shocking turn of events, Borsalino once again came out on top.
As the eater of the Pika Pika no Mi, the only one of the three original Admirals from the beginning of the series to still hold his position has complete mastery over light and, as such, is the fastest character in One Piece. Combined with strength that's at least close to the level of Sakazuki and Kuzan's, and extreme versatility, Borsalino can defeat almost anyone, and easily outlast low-endurance opponents like Gear 5 Luffy.
Former Fleet Admiral Sengoku is as Past His Prime as Garp
Even in his prime, former Fleet Admiral Garp was never quite on the same level as his best friend Monkey D. Garp, or their mutual rival Gol D. Roger. There's no shame in not being as powerful as two of the strongest characters in the entire verse, though, and, even past his prime, Sengoku was still a force to be reckoned with during the Marineford Arc.
The eater of the Hito Hito no Mi, Model: Daibutsu, Sengoku used his giant Buddha form to challenge the entirety of the Blackbeard Pirates, sending them flying with his shockwaves. In his base form, he was also capable of injuring and knocking down Garp. Additionally, unlike every other Admiral, Sengoku is known to possess mastery over all forms of Haki.
Former Admiral Aokiji Defeated Garp During Their Emotional Clash
The first Admiral fans ever saw in action, former Admiral Aokiji, now simply known as Kuzan, set a bar that few of his peers have ever been able to match. Having eaten the Hie Hie no Mi and trained under Garp, Kuzan is both a god of ice, and one of the fiercest hand-to-hand combatants in One Piece.
During the timeskip, Kuzan fought Sakazuki for 10 days on Punk Hazard, terraforming the island in the process, and only barely losing. More recently, Kuzan stunned fans everywhere when he defeated his mentor Garp in a raw brawl, while actively holding back.
Fleet Admiral Akainu is an Endgame One Piece Villain For Luffy and Sabo
Despite not having even fought post-timeskip, it remains clear that Fleet Admiral Akainu, also known as Sakazuki, is still the strongest of all the Admirals. While he isn't known to possess Conqueror's Haki, he is in his prime, unlike Sengoku, and his victory over Kuzan at Punk Hazard is what made the master of magma Marine Fleet Admiral in the first place.
Besides his rank and his victory over Kuzan, Sakazuki has also very obviously been set up as a major antagonist for the very end of the series. His murder of Portgas D. Ace established him as one of Luffy's greatest enemies and, when the final war occurs, it'll likely be both Luffy and Sabo who face him, eager to avenge their fallen brother.
