Every example of Arknights dura negation is just bypassing heavy armor that physical damage normally. Heck, that's what's provided as an example on the profile
But Charizard is naked, he's not wearing heavy armor, and he doesn't get defensive stat boosts either
It's like Charizard taking damage from a regular attack, and
Chip Away,
Sacred Sword, and
Darkest Lariat, or any move boosted by Unseen Fist. All 3 of those moves and the ability "ignore armor" since they bypass standard means of protection, but Charizard takes the same amount of damage from all of those moves since he doesn't have any armor to penetrate. It's just skin and flesh
Mega evolving increases Charizard's durability, but not artificially. His very biology changes. I don't think the dura neg can bypass the defenses provided from a literal mutation