Kyojuro Rengoku surpasses Tengen on many levels, be it strength, Breathing Technique, or battle Intellect. So to cut a long story short, Kyojuro Rengoku is more powerful than Tengen Uzui.
Tengen Uzui is the second strongest Hashira in physical strength, only being surpassed by Gyomei.
But, when it comes to who was the better Hashira, Tengen wins by a considerable margin. His experiences as a shinobi and as a Demon Slayer far exceeded Rengoku's, and led to him developing far superior strength, battle tactics, and techniques.
As a result, Tengen Uzui has to deal with the moniker of being the least powerful Hashira around. Of course, that's not the worst thing in the world, as all Hashira are strong. He's still incredibly powerful and can give any demon a run for their money.
The respective fights of the Hashiras with the demons are also proof that Rengoku will win in the Tengen vs Rengoku fight. He was single-handedly able to fight Akaza, an upper rank 3 demon, and almost win the fight.
Despite being the lowest of the Upper Ranks, Gyutaro showed much of his demonic prowess by making Tengen lose his left arm and his left eye in battle. However, Giyu would have been a better opponent for the demon and could have defeated him without losing any limbs.
1/8 Would Lose: Tengen Uzui Can't Counter Akaza's Compass Needle.
Despite her petite appearance, Mitsuri Kanroji has a special muscular composition that makes her muscles eight times denser than an ordinary human's. She is also more flexible than the other Hashira. These two strengths balance out her being the slowest runner out of all the Hashira.
2) Sanemi Shinazugawa
He dedicated all his time and effort towards perfecting his skills as a swordsman which was shown during the fight against both Muzan and Kokushibo.
Nezuko setting Tengen on fire. By the end of the battle, Gyutaro's poison has spread throughout Tengen's body resulting in his inability to speak. As he lays dying from the poison, Nezuko Kamado intervenes and uses her her Blood Demon Art to burn the poison out of his system, allowing him to rejoice with his wives.
Gyomei Himejima is the strongest Hashira in Demon Slayer because of his raw power and adaptability skills during battles. In Chapter 134, Hashibira Inosuke claims he is “The Strongest Demon Hunter” and explains how the sight of the Stone Hashira gives him the chills.
3 Hashiras that can beat Rengoku in Demon Slayer
Gyomei is considered to be the strongest Hashira in the series. His contribution was monumental in the battle against Kokushibo and Muzan.
So to cut a long story short, Kyojuro Rengoku is more powerful than Tengen Uzui. Among the Demon Slayer Corps, Kyojuro was acclaimed as a skilled combatant who was always dedicated to fulfilling his duty as a Hashira. Tengen admires and respects Kyojuro for his dedication to protecting human lives.
In terms of physical strength, Tengen Uzui is far from being the weakest Hashira. While his feats throughout the Daki and Gyutaro battles certainly displayed this, there's additional evidence to show that he's not the weakest Hashira.
Despite his incredible strength and heroic efforts, Demon Slayer's Tengen Uzui needed a lot of help to defeat Gyutaro. Upper-Rank Six proved to be no pushover in the "Entertainment District" arc, nearly claiming the life of a Hashira from beyond the grave.
2) Sanemi Shinazugawa
His fast movement, combined with his excellent swordsmanship, makes him a remarkable demon slayer. Most of his attacks are purely offensive due to his breathing style. Being a user of wind breathing, he is undoubtedly fast.
5/14 Fastest Hashira In Running
Despite his large and muscular build, Tengen Uzui is the fastest runner among the Hashira.
1) Shinobu Kocho
The Insect Pillar of Demon Slayer Corps, Shinobu is undeniably the smartest individual. She might not be physically stronger than others, but her intelligence is what kept her going.
Tanjiro decapitates Akaza with the Hinokami Kagura: Setting Sun Transformation. Akaza was bewildered, wondering how Tanjiro did not have any fighting spirit, comparing this feeling to fighting against a plant. He acknowledges that Tanjiro surpassed his speed.
Giyu Tomioka and Sanemi Shinazugawa attend as the final surviving members of the Hashira, and together they they get a confirmation that not only are the demons all eradicated, but that the Demon Slayer Corps will be disbanding.
Yoriichi was born with the Demon Slayer mark and prowess in swordsmanship. His powers were beyond comparison as he defeated Muzan once and had him on the verge of death until he managed to escape.
During his battle with Gyutaro, Tengen used his muscles to stop his heart to temporarily prevent the poison from circulating, which let him get the drop on Gyutaro who believed he was dead.
At the end of the day, none of the Hashira could've defeated Akaza – even though a few of them could've succeeded in decapitating him. Akaza proved himself to be too strong to be dragged into sunlight, meaning there'd be no way for any of the Hashira to kill him.