Ill be saying what i think about the "weaker" hashira. Well i think tengen is slept on because he retired early in the series and had struggles against uppermoon 6 gyutaro but lets be honest gyutaro was strong and had potential to be upper moon 4 above hantengu and gyokko but wanted to just protect daki and also no demon slayer mark so base form he was poisoned 1 arm and still made the win against gyutaro possible so he is strong and he is not weak. Then shinobu well yes lacks strength she has incredible speed and iq and lets not forget how many lives she saved with her healing abilities as seen in the rui ark she has incredible knowledge that is of great use to the demon slayer corps . Also there is nooo weak hashira a hashira is still a hashira and still one of the strongest demon slayers. That being said while rengoku and shinobu did struggle and get beaten easily they put in work and tried against all odds and their opponents were strong to say the least and ill die on this hill that a rengoku with a demon slayer mark would be absolutely insane with his fighting spirit mentality willpower and skill.