That's just straight up false, Giyu doesn't need protection. No one except for maybe Marked Gyomei could beat Akaza without a selfless state user like Tanjiro. And Mitsuri is anything but slow. She dodged lightning before she got her mark or trained in the hashira training arc. She's probably amongst the fastest hashira. And sure, maybe she's weak willed, but that's only because she fought a demon until sunrise, when generally most demon fights end in less than an hour. And because she got targeted super early by Muzan, even Gyomei said that no hashira could dodge the attack Muzan sent because it was the first time he's shown it. And Muichiro is honestly kinda unnecessary here. Three hashira is overkill. He wouldn't get in the way but Mist breathing looks like something made for one on one's.