Actually, it is required. That's because Big Mom is not as durable as Kaido and there are different types of attacks and at different levels.
Big Mom durability has never been hyped to or portrayed at Kaido's level. Big Mom's body has been described as an iron balloon. Zoro cut steel pre TS. His non-haki dragon twister cut steel/iron turtle shells during FMI arc.
While Kaido's body has been described as being invincible. He couldn't be killer by execution or suicide.
Once again there's no proof that they attacked them with Ryu/internal destruction haki. The scene even shows Luffy attacking in base when he was out of haki. Think about that. Luffy knew that attack wouldn't work but he still attack. That was a complete waste of time and energy.
Kid was the one saying their attacks wasn't working.
Big Mom was scared of Zoro's flying dragon blaze and that was before he proved he could cut Kaido. That tells us how well her durable body would (not) have handle Zoro's ryu attacks.
Asking for facts is now considered moving the goal post.
Pathetic.
You claim they all weren't holding back. Yet, Zoro didn't use asura mode until after he blocked Hakai and Big Mom left the rooftop. While Kid and Law didn't use awakening at all on the rooftop. That proves they were holding back and you contradict yourself with your own post.
The group (5SN) attacking Big Mom and Kaido doesn't mean each individual SN attacked Big Mom. Even if they that still doesn't prove Luffy used internal destruction haki or Zoro used ryu. It's like being part of a group project. Just because everybody helped out with the entire project doesn't mean everybody helped with each part of the project.
Look at Zoro vs King. The manga showed us King has stronger defense than Kaido. Even then Zoro didn't use haki with every single attack against King.
Neither you nor anybody else have any facts supporting the claim Zoro or Luffy used haki attacks against Big Mom and that's the only truth.