I don't think any of the hashira is stronger than Tanjiro by the end of the series, he's easily the Strongest
In his own franchise, Tanjiro is outclassed by most of the nine Hashira as of the end of season 1, including Giyu Tomioka. It's easy to compare Tanjiro's strength to Giyu's — since they are both demon slayers — and they even use the same element: water.
That being said, Tanjiro's rank is unknown, and his rank was last revealed in the Entertainment District arc. In that arc, they were at Kanoe, which is fourth from the bottom. Since Kiriya Ubuyashiki announced the disbanding of the organization, Tanjiro doesn't get the chance to become a Hashira.
Tanjiro's Current Demon Slayer Rank Is Kanoe
Not many of the Demon Slayers' ranks are known as of Season 2, but there are a few. Tanjiro, Zenitsu, and Inosuke have moved from Mizunoto up to Kanoe due to their exploits.
His diamond-hard skull might be advantageous in certain situations, but he doesn't need to resort to headbutting after he unlocks the long-lost art of Sun Breathing. Despite his young age, Tanjiro can be considered the strongest Demon Slayer still alive in the story.
Muichiro Tokito – Mist Hashira
In direct combat, he easily overpowered our protagonist Tanjiro so his strength is not to be taken lightly. Another testament to his skills is his win over Gyokko, an Upper Rank Five demon, whom he defeated all by himself – too with ease.
The Thirteenth Form of the Sun Breathing Style is unique in the sense that it doesn't really have a name of its own. Rather, it's a combination of all the twelve forms present in this style, used in succession to maximize their power. This move was devised by Tanjiro solely to defeat Muzan.
Giyu is one of the first Hashira introduced in Demon Slayer. He plays a vital role in Tanjiro's development and is the main reason Nezuko is allowed to stay with him.
Tanjiro's superhuman strength gives him the ability to overpower his enemies and dodge attacks at immense speeds, he is able to maneuver and jump easily over large buildings and distances thanks to his amazing strength.
Nezuko is at least stronger than Daki, meaning that if Muzan could bring her back under his control, she would certainly qualify for the most prestigious title a demon can hold: a member of the Twelve Kizuki. Thanks to Nezuko's remarkable strength, she would have to be an Upper-Moon.
Unfortunately, the answer to this question would be, no, he did not. Zenitsu, along with Tanjiro and Inosuke got way stronger than average corps members with training. In fact, he became one of the very few to even invent a new form of Thunder Breathing. However, his dream of becoming a Hashira was never realized.
13th form Tanjiro simply blitzes Akaza. In that form, he's relative to WH Muzan in speed who is faster than all the UMs.
Regardless Zenitsu's power rivals those of the Hashira. Having the ability to fight unconscious and fight while awake to face one of the upper ranks is a sight to behold. There is more to Zenitsu than is insane strength and power. Zenitsu has impressive hearing, similar to Tanjiro's remarkable sense of smell.
Gyomei Himejima, the Stone Hashira, is the strongest Hashira in the Demon Slayer corps in terms of strength and swordsmanship. He is the only person who uses spiked flails and an axe instead of standard swords to kill demons. Such a weapon takes immense precision and soundness to use without inflicting personal damage.
Tengen Uzui
He is the fastest Hashira, and the second physically strongest. Obviously, then, Tengen Uzui is rather proud. He is demanding, fussy, boastful, and prone to selfishness. But he is also ultimately kind and caring, with great love for his three wives as well as the other Hashira.
Thanks to the Demon Slayer data books, we don't have to wonder who the strongest. or fastest Hashira were in the series. Like, did you know that Mitsuki Kanroji. is the slowest Hashira, despite the fact that the data book says she ate.
Towards the final arcs of the manga, Tanjiro is mortally wounded and dies during a fight with the Demon King Muzan. Though Muzan is also seriously injured, he uses the last of his powers to turn Tanjiro into a demon.
With all said and done, Tengen Uzui is one of the strongest and most extremely skilled Demon slayer in the series, his physical abilities, combat skills and strategic thinking makes him a tough opponent to defeat in a battle.
On the other hand, Sun Breathing can, presently, only be performed by Tanjiro Kamado. Though its techniques can be taught to others provided they have the guidance of a Kamado, there are no other known users who are currently alive.
This anime repeatedly shows viewers the clear difference in the strengths of demons and humans, and that teamwork is the only way to overcome a task that seems insurmountable. In conclusion, Tanjiro will not be able to kill Muzan by himself since the Demon King is far superior in every aspect of combat.