Gyomei's raw strength and ability to use Transparent World makes him the strongest Hashira and therefore, he is leagues above Rengoku.
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.
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.
Gyomei Himejima is the strongest Hashira in Demon Slayer. This fact has been established in the manga as Tanjiro, Inosuke and Zenitsu all agree that he is the strongest member of the Demon Slayer Corps.
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.
1. Gyomei Himejima – The Stone Hashira.
Rengoku fought Akaza in the Mugen Train arc of Demon Slayer. The Flame Hashira gave his all trying to protect the ones around him, and he succeeded. He almost succeeded in decapitating Akaza's head by using his Esoteric Art.
Gyomei's raw strength and ability to use Transparent World makes him the strongest Hashira and therefore, he is leagues above Rengoku.
He would be disoriented by the shockwaves created by Akaza's blows. Tengen has anti-demon bombs that can disorient them for a short period of time, but this wouldn't be an effective strategy when Akaza uses Compass Needle, which allows him to accurately pinpoint and aim for his opponent's weak spots.
Shinobu Kocho Is the Weakest Hashira
Of the three Hashira who were killed by Upper-Ranks -- Rengoku, Shinobu and Tokito -- Shinobu was the only one who was killed almost instantly when she encountered Doma, Upper-Rank Two.
Rengoku's Unwavering Will Was His Greatest Weakness
Since he believes it is his responsibility as someone strong to protect those weaker than him, he will make sure he does just that. Rengoku sees any mission through to the very end, even at the cost of his life.
After awakening his demon slayer mark, Giyu greatly overpowers Akaza. However, he is able to keep up with the fight only because of Tanjiro. If Giyu had soloed against Akaza, he would have died.
In terms of feats, Zenitsu manages to go all out (to the point of exhaustion/almost death) to one-shot a Upper Moon Six, while Rengoku manages to go toe to toe with a Upper Moon Three, only losing because his opponent could regenerate while he could not. I give it to Rengoku here even though Zenitsu is my favorite.
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.
In conclusion, Nezuko cannot beat Akaza in Demon Slayer. In terms of power, physical abilities, regeneration rate and overall combat ability, Akaza is far superior compared to Nezuko.
Akaza wanted to make Rengoku a demon so that they could fight for hundreds of years, so that they can both continue to grow stronger. Akaza genuinely admired Rengoku's strength, and was impressed with his skills. Despite that, he knew that Rengoku wouldn't realistically be able to defeat him as a human.
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.
Kyojuro Rengoku (煉獄 杏寿郎) 5695. 1601.
Sanemi's blood is known to be enticing yet intoxicating to Demons, which he used to bait and stab Nezuko. Sanemi is clearly the least popular Hashira among Demon Slayer fans.
Tengen Uzui
This Breathing Technique gives him echolocation and other advanced hearing abilities. Even though he is large and muscular, and uses that to his advantage, his fighting style relies more on aesthetics and flashiness. He is the fastest Hashira, and the second physically strongest.
As a Hashira, Tengen possesses incredible strength, speed and agility which allows him to fight at super-human levels, as he is the sound Hashira, he also possesses incredible hearing abilities and uses sound waves to locate his enemies and to listen and beware of his surroundings.