Hmm
Then maybe you can make it similar to how like Gajeel Steel Dragon Slayer move is above his normal attacks and one shot:
Comparable to Lightning Fire Dragon Mode Natsu after it's initial usage),
higher with Steel Dragon's Sword (One-shot
Super Armor Etherious Form Torafuzar)
So in the case of Kiria and Erza
Kiria: Fought and matched X793 Strongest Armors Erza
Erza: Fought and matched Kiria,
higher with Dragon Slaying Sword Belserion ( one shot Kiria, comparable to X793 Base Laxus )
Does that make sense?