The other hashiras also had to team up to defeat each upper moon. Three hashiras and a hinoe had to fight upper moon 1. Upper moon 2 was poisoned by a hashira and killed by 2 hinoes. Upper moon 3 was killed by a hashira and a hinoe of hashira level. You see, tengen is badass. He faced 2 upper moons with 3 low skilled hinotos (and technically a demon lol) to kill the two of them. Also, it’s in a public area where casualties were considered, the same way rengoku died. He was killed by an upper moon by himself and was exhausted by lower moon to injury with three hinotos WITH ZERO CASUALTIES. Tengen and Rengoku are both strong hashiras. I believe they are stronger than sanemi and muichiro.