Some people think that Kokushibo is stronger than Doma, Akaza, Hantengu, Gyokko AND Daki & Gyutaro combined, that all 5 of the mfighting together are weaker than him alone. Let's challenge this assumption a little bit.
It took Genya, Muichiro, Gyomei and Sanemi to take him down.
So, let's make this squad fight upper 2-6 at once.
Gyomei can 1v1 Doma because he is very strong. However, Doma's blood demon art is extremely powerful because he has so many clones, frosty air, insane speed, etc, so Gyomei is not really stronger than him and the only reason he stands a chance is Doma's lack of seriousness and the fact he does not really care about anything. While they fight, since doma's frosty air might spread to other places, which would impact other fights negatively for other demon slayers. But let's assume they are far away from the rest of the fight
Sanemi could try a 1v1 against Akaza. However, he is very angry and has a lot of bloodlust, which Akaza will exploit with his compass. He is unlikely to figure it out. Also, some people might argue that he could keep up with Kokushibo alone. Yes, it is true, but not forever and also Kokushibo was not going full power when they were in a 1v1. It took 2 marks on top of Tanjiro's red blade, see through the world and selfless state to beat him (and Sanemi is unlikely to unlock this) to beat him and even then it is possible Akaza regrows his head.
Genya can try to fight Hantengu, but in the manga he needed the help of one marked pillar, marked + red blade Tanjiro and nezuko, he is not winning alone when the fight was so close even with all the help. Genya dies here.
Muichiro is strong, but he cannot fight 2 upper moons at once. He got blitzed by casual Kokushibo, he does not have the strength to fight both Gyutaro and Gyokko at once (one small mistake and he is done). Even if he kills both of them he most likely dies of poison because fighting 2 upper moons at once is too much.
Hantengu can then go back Doma up (Doma does not get defeated quickly, he is very op). Gyomei cannot win against Doma and Hantengu at once and dies.
Even if Sanemi somehow wins he is not going to survive both Doma and Hantengu.
So as you can see a group strong enough to take Kokushibo down cannot beat the rest of the upper moons combined.
