Shanks loses his arm because of a Sea King, despite being one of the strongest characters in the series. Therefore, it somehow ends up being a plot hole, making fans question Oda's decision even now.
In fact, Luffy easily defeated one at the end of the very first chapter. Shanks is a Yonkou, who are highly regarded as the strongest pirates in the seas. One Piece fans still disagree about how the Sea King managed to bite off his arm in the first place.
long story short, shanks purposely gave up his arm to instill trauma to luffy about what would hapen if he tried to be a pirate with halfassed resolve and full of weakness, he'll unable to protect something or someone important to him, and it's seem that shanks action works like a charm, since luffy is a lot more ...
The level of strength of Haki determines what kind of attacks it can block, which is why 12 years ago, Shanks was unable to block the attack from the Sea King, as he was not at the level of strength that he is now.
Being a Sea King, the Lord of the Coast is naturally a very vicious and dangerous predator, as well as a powerful swimmer. His will is weak enough to be affected by Shanks' Haoshoku Haki, having been intimidated by him.
However, there is one particular scene with a hidden mythological reference, and it remains one of the most impactful scenes in the series. Shanks loses his arm because of a Sea King, despite being one of the strongest characters in the series.
According to Brannew, Mihawk's swordsmanship skills are known to exceed even those of red-haired Shanks. Therefore, in terms of swordsmanship alone, Mihawk is certainly better.
As noted by the Five Elders, Shanks is a pacifist by nature who does not actively seek to cause chaos and disorder.
One Piece finally reveals the secret of Shanks' incredible power, and it lies in his mastery of Observation Haki and his ability to see the future.
Shanks possesses the ability to use Kenbunshoku Haki, as revealed in his vivre card and has almost unrivalled mastery over it. He is known for being the Killer of Observation Haki as he is able to stop people from being able to use it as seen from Kidd.
Whilst in Foosha Village, Shanks found Luffy to be an incredible and endearing kid, so much so that he gave him his precious straw hat as a sign of his faith that he will become a great pirate.
Firstly, before the Wano Arc, the Kid Pirates initiate an attack on Red-Hair Pirates. Shanks' crew only responds to the immediate threat by defeating Eustass Kid and cutting his arm off. This is letting him off easy compared to the brutality of the pirate world.
He said that he wanted to speak to them about a certain pirate. Who that pirate is wasn't explicitly mentioned, though it is likely one of two pirates.
Shanks has clashed against Kaido when the latter tried to reach Marineford. It is very likely that Shanks would be able to injure Kaido in this battle.
It was Marshall D.
For reference, manga readers can look up Chapter 434, while anime viewers can watch Episode 316. It turns out that Shanks got his scar from Whitebeard's former crewmate, Marshall D. Teach.
The narrative doesn't fit that he came to rescue Ace or help the Whitebeard pirates. He came to stop more pointless deaths. If so, he'd have simply gone to Marinefold from the beginning. Rather, he went to prevent Kaido from turning the war into more of a bloodbath.
Fans were introduced to this ability through Charlotte Katakuri during the Whole Cake Island arc. According to Bege, Katakuri had trained his Observation Haki to a level where it allowed him to see slightly into the future.
Roger used advanced forms of conqueror's haki as he imbued his sword with conqueror's haki and clashed with Whitebeard. He also used advanced armament haki for more powerful sword attacks. Additionally, Roger possessed the observation haki, thus, making him the strongest haki user of all time in One Piece.
As a Yonko, he is extremely powerful and feared around the world. He is a very obvious reference to a famous Viking pirate named Erik the Red. However, aside from that, Shanks' character is heavily inspired by the Greek god Tyr, known as the patron of warriors and mythological heroes.
This, together with a line from the movie (whose story is canon for the series), in which the Five Elders say that Shanks belongs to the "Fearland Family", seems to confirm that Shanks is, in fact, a descendant of the Celestial Dragons, the all-powerful families who hold absolute authority over the world.
It's entirely possible Mihawk noticed through their duel and training that Zoro suffers from ocular dominance in his left eye. That is to say, the left eye is stronger than the right. As a result, maybe Mihawk scarred the left eye shut and instructed Zoro not to open it until his right eye was trained enough.
Shanks is probably way above Zoro`s level. Of all the characters still alive in One Piece, Dracule Mihawk is undoubtedly the strongest swordsman in the world. After all, he holds the title. Vista was the commander of the fifth division of Whitebeard`s Pirates and was considered the best swordsman in Whitebeard`s crew.