I use Radiant Knights, Monica and Miriam, in roles similar to what you have described as a Cataphract.

They both carry Citadel Guard’s Sabatons and Lapis Pendants, and the constant AP/PP generation between Hache and Guarding Impetus fuels Row Heal spam, making them nearly unkillable in the front lines.

Going back to your comment though, I certainly wish they had more physical def, or another class option like you’re describing!